Saturday, June 28, 2014

The Superlative Land of Strange Standing Stones (Part III): Bryce Canyon National Park

One of the mysteries of the origin of the Grand Canyon involves the fact that early rivers flowed in the opposite direction of the Colorado River that exists today. Some of those early rivers ended in lakes that covered hundreds or thousands of square miles, and the deposits from those lakes form some of the most vividly colored rocks on the Colorado Plateau. And it's not just the color.. Erosion has sculpted the freshwater limestone of the Claron Formation into one of the craziest landscapes in North America.

Welcome to Bryce Canyon National Park, part III of our tour through the Land of Strange Standing Stones. In the first entry, we were checking out strange erosional forms left after groundwater moved through crushed rocks on the Cockscomb Monocline along Cottonwood Wash Road. In the second, we explored the strange sedimentary pipes of Kodachrome Basin State Park. We've now moved a few miles west onto the Paunsaugunt Plateau, one of the faulted mesas in the High Plateaus province of the Colorado Plateau. Headward erosion along the edge of the plateau has produced the bizarre landscape of Bryce "Canyon" (there is no actual canyon; the park is instead a series of erosional amphitheaters).
Natural joints and fractures in the limestone are exploited by water and ice, producing the pillars of stone called hoodoos. The rate of headward erosion is rapid, amounting to feet per century. Many places in the world erode this way, but few if any display the sheer number of fins, spires and hoodoos. There are tens of thousands of them in the park.

Sometimes people on a strict schedule visit the park, go to a single viewpoint and say "okay, hoodoos and Bryce Canyon checked off the life list", and rush on to the next park. One can miss some pretty incredible things by doing so. For one, the tour buses rarely go past Inspiration or Bryce Points. The views are spectacular at the main tourist parking lots, but the main park road goes fourteen miles farther, past nearly a dozen other viewpoints.
View north from Rainbow Point

Rainbow Point, for instance, is the highest viewpoint in the park (at 9155 feet, it is a thousand feet higher than the more popular viewpoints). From it and adjacent Yovimpa Point, one has an incredible view extending from the Wasatch Front to the north, Navajo Mountain to the east, and the North Rim of the Grand Canyon to the south (part of the view from Rainbow is seen above, and Yovimpa Point is below).
View southeast from Yovimpa Point, towards Navajo Mountain and the north rim of Grand Canyon
Likewise, Natural Bridge is an incredible 85 foot arch that is missed by many park visitors who don't venture beyond the busier parking lots. Every time I mention the feature I feel compelled to point out that natural bridges usually have watercourses of some kind. This one is best described as an arch.

And then there is the fact that every viewpoint at Bryce Canyon is on the rim, which means that every tourist who visits only the viewpoints is an outsider looking in. There is nothing quite like walking among the towering rocks and seeing them from below. I didn't walk below the rim on this particular trip, but I encourage you to check out my post from a previous trip, when I walked the Navajo Loop through Wall Street Canyon. It includes some of what I think are my best ever pictures from Bryce Canyon.
There are also the animals. I caught a nice Say's Phoebe at Natural Bridge (above), and we saw a small herd of Pronghorn Antelope in the woods and meadows back of the rim.
There is a colony of Utah Prairie Dogs next to the park road, and I've had no luck catching a picture of any of them for years.

We didn't have any such adventures on our latest trip, but I must say there is nothing quite like experiencing the summer monsoons of Bryce Canyon. In July and August, moisture-laden air moves north out of the Gulf of Mexico, and sweeps up against the plateau margins, producing spectacular thunderstorms and flashfloods. One of our family memories involved a terrifying lightning storm and cloudburst that produced a lake in our tent, and a six foot wide river below our campsite just a few hundred feet from the rim.

Bryce Canyon is worth a second look if you've ever rushed through in the past, and if you've never seen it in person, make sure to make the time to really explore it! Pictures just don't do it justice.

Friday, June 27, 2014

A Land of Strange Standing Stones, Part 2: Kodachrome Basin State Park

There was a time not all that long ago when there was a part of the United States mainland that was still considered terra incognito. It was in 1948 that National Geographic explored this region and called it not a tour, but an expedition, complete with jeeps and supply caches, and explorers who gave new names to features, even though many of them already had been named by the resident ranchers.
Kodachrome Basin State Park (once called Thorley's Pasture) in southern Utah showed up at the end our our 40 mile gravel road journey through what I called a land of strange standing stones (it's also accessible from the north by a paved road out of Bryce Canyon National Park). For the second time in a day we were treated to the strange sight of vertical pillars of stone, but these had an origin quite unique from the spires along  Cottonwood Wash Road. It's an origin so unique that geologists haven't quite decided what it actually is.

The spires, called sedimentary pipes, are composed mostly of a mix of sediment from the lower members of the Carmel Formation that have penetrated into the overlying Entrada Sandstone. There are more than five dozen of them in and around the park, ranging in height from 6 feet (2 m) to 170 feet (52 m). They are composed of a more highly cemented rock, having been exposed as the surrounding sediments were eroded away It has been suggested that they are the result of hot spring activity, and that they might have been pathways for geysers (some have suggested that the park is sort of a Yellowstone in reverse). This is an intriguing and imaginative idea, but what was the source of the heat? There are no magma intrusions in the immediate region, and in other parts on the Colorado Plateau where intrusions do occur, such pipes aren't found.

Another possible explanation is that the pipes are liquefaction features, places where water rushes towards the surface from saturated layers below during the shaking from earthquakes. I like this explanation, since there are some major fault zones just a few miles away. But researchers say there is a time problem. They say that the pipes are very old features: they don't penetrate the overlying Henrieville sandstone, and are therefore probably Jurassic or early Cretaceous in age. The faults in the region didn't become active until less than about 15 million years ago. Maybe.

The most recent hypothesis is that the pipes formed from lenses of groundwater trapped in sabkha deposits, layers of evaporites like salt or gypsum along arid environment shorelines, which formed the Paria member of the Carmel formation. As younger sediments were laid down on top of the older layers, the pressure grew in the groundwater deposit, and water squeezed out, following the path of least resistance, generally upwards. This model is interesting, but has it been seen in other settings? Some of the petroleum geologists that have traveled with us find this to be a  plausible explanation.

But aren't mysteries great? Like the origin of the Grand Canyon, science thrives on unanswered questions. It's a fascinating place to visit and explore.
The sediments in which the pipes occur are mostly members of the Jurassic Entrada formation, which is responsible for some spectacular scenery in other parts of the Colorado Plateau, most notably at Arches National Park and Goblin Valley State Park. The bright orange layers are the Gunsight Butte member, while the high white and red striped cliffs are the Cannonville member, and the light tan layers are the Escalante member. The highest cliff ramparts are composed of Cretaceous Henrieville and Dakota sandstones, last seen at Grosvenor Arch.

For more information...

Get the park brochure here:

An excellent resource: Baer, J. and R. Steed. 2010. Geology of Kodachrome Basin State Park, Kane County, Utah. In Sprinkel, D.A. et al (eds.), Geology of Utah's Parks and Monuments, Utah Geological Association Publication 28, 3rd edition. Salt Lake City: Utah Geological Association, 467-482.

Tuesday, June 24, 2014

A Land of Strange Standing Stones, and an Odd Connection to the Grand Canyon

There are a lot of strange landscapes on the Colorado Plateau and otherworldly scenes. Some are famous enough as to not surprise first time visitors, such as the spires and hoodoos at Bryce Canyon National Park. But others are hidden, strung along gravel roads far off the beaten track. Seeing them for the first time comes as a shock. These rocks just aren't "normal". 
The largest single park in the Colorado Plateau region is also one of the least familiar. Really, how many of you have heard of Grand Staircase-Escalante National Monument? It covers a huge swath of land north of Grand Canyon and Glen Canyon National Recreational Area, west of Capitol Reef National Park, and south of Bryce Canyon. It was controversial in its birth, as have been most of our National Monuments, but it is indeed worthy of protection. We are only just beginning to discover the treasures that lie within its borders.

Our journey on this day would take us from Glen Canyon Dam to Bryce Canyon National Park via Cottonwood Wash Road, a gravel track that runs for thirty miles along the East Kaibab Monocline, known here as the Cockscomb.
Part of the Cockscomb (East Kaibab Monocline) courtesy of Google Earth
A monocline is a step-like fold, flat on either side and flexing in the middle. Such folds often develop where fault moves beneath horizontal sedimentary layers. The Cockscomb is an extraordinary example of one of these features, with a vertical separation of nearly a mile (erosion has leveled off much of the uplifted rock, so the actual elevation change across the fold is much less). The fold is also very long. It extends for 150 miles and actually forms the eastern edge of the Kaibab Plateau where the Colorado River turns west to form the deepest part of the Grand Canyon. It formed during the Laramide Orogeny in Late Cretaceous-Early Paleogene time.
From Wikipedia
The rocks within the monocline have been twisted so much that the layers are vertical. They have also been attenuated (stretched) so that some of the layers are thinned out. The rocks have been brecciated (crushed) to some extent, which provides a probable explanation for the strange towers and pinnacles found here and there along Cottonwood Wash Road. Groundwater following the fractures would have left mineral deposits that had the effect of reinforcing and cementing some of the most deformed rocks. Erosion removed the surrounding softer rocks leaving behind the towers and spires.

Pareidolia is the tendency of humans to build patterns out of randomness, seeing things that aren't really there: faces in clouds, and human or animal figures in rocks. Who does the rock below bring to mind?

The final rock in our little mini-tour of the Grand Staircase is Grosvenor Arch, which is really two arches, and which once was called Butler Arch until people on an expedition with the National Geographical Society decided to name it after their boss. They apparently had more pull with the Board of Geographic Names. It's not part of the monocline, but is instead at the boundary between two layers of different erosional resistance. The upper rock is a conglomerate equivalent to the early Cretaceous Cedar Mountain Formation, while the lower layer is the Henrieville Sandstone of Jurassic age. The largest opening is 152 feet high and 100 feet wide.

Lastly I have pictures of flowers. Despite the ongoing drought, there were some beautiful wildflowers blooming in one of the side canyons we explored. There were Evening Primroses...

...and some beautiful Sego Lilies, the state flower of Utah.

Monday, June 23, 2014

Too Much Dam Hubris...Lake Powell and the Future of the Colorado River

The Colorado River is a wonder of nature. Starting from glacial cirques high in the Rocky Mountains, the river flows through one canyon after another, culminating in the grandest canyon of them all, the Grand. For 1,450 miles, the river is a corridor of life, and webs extend out in numerous directions, providing life in some unlikely locations, like Las Vegas, Los Angeles, and Phoenix. Irrigation from the Colorado grows vast amounts of crops in desert valleys throughout the southwest.

The river has exposed an incredible geological story, and has played an important part of my life in my development as a teacher and geologist. It was a catalyst in my own life as I explored a corner of it on my first geology trip, and more recently as I floated a raft through the Grand Canyon for the first time last summer. So it is that I feel a little bit of ownership of the river (along with about 35 million other people).
I first became aware of the abuse of the river system as a teen when I came into possession of a dogeared copy of On The Loose, by Terry and Renny Russell, which was in part a eulogy for the canyons that disappeared beneath the stagnant waters of Lake Powell, backed up behind Glen Canyon Dam. I had grown up learning of the giant mega-dams as the greatest achievements of mankind (did anyone else get taught "Roll on Columbia, Roll on" while in grade school?), and I was duly impressed when I saw Lake Mead and the newly completed Glen Canyon Dam when I was a child on vacation. I started to learn that there were more issues at stake in regards to these giant mega-dams. Yes, flood control. Yes, cheap renewable clean energy. But at the cost of the some of some of the most amazing scenic canyons in existence, and at the cost of an entire river ecosystem. I know that those arguments don't hold much sway in a capitalistic society that measures the value of something in dollars earned. The thing is, the main purpose of these dams is imperiled by changing climate. One has to wonder if they were a gigantic mistake in the end. Do the benefits truly outweigh the costs?
One of the most incredible stories of Glen Canyon Dam is that it came perilously close to failing during an extraordinary runoff event in 1983. I've covered this story in the past, but it bears repeating (especially if you not familiar with it). Instead of using floodgates and spillways at the top of the dam for emergency drainage, designers utilized the diversion tunnels used to channel the Colorado River around the dam site during construction. They proved woefully inadequate to the task in 1983 as cavitation caused the walls of the diversion tunnels to rip out. In places the powerful flow of water cut 32 feet (10 meters) into the soft Navajo Sandstone and threatened the structural integrity of the dam itself. The diversion tunnels had to be shut down, and the lake threatened to flow over the crest of the dam in an uncontrolled fashion. This could have led to catastrophe, as such uncontrolled flow could have eroded and weakened the sandstone abutments of the dam. Failure of Glen Canyon dam would have led to the domino-like destruction of other large dams downstream, and the decimation of the water-supply infrastructure of some thirty million people. The disaster was averted by the construction of an 8 foot high dam of wood flashboards that held back the water long enough for the flood to subside. The structural integrity and survival of the dam came down to about one inch...the distance between the water level and the top of the flashboard dam in 1983.

There is an inherent conflict between water storage for irrigation and energy production, and flood control. One requires a reservoir to be mostly full; the other requires sufficient storage space for unusual events like those of 1983. The conflict requires a balancing act on the part of the water masters. Getting the balance wrong can lead to catastrophe downstream.

The scary part is that the 1983 event was not actually all that unusual. It happened because of a lack of storage space in the reservoir at the time (it had filled for the first time ever in 1980). The flooding involved flows of over 111,500 cubic feet (3,160 m3) per second. This was statistically a 25-year flood, one that has a 4% chance of occurring in any given year. Unfortunately, the statistics that guided the design of the dam have been called into question because of analysis of flood deposits upstream near Moab, Utah. New research suggests that there have been more than 40 large floods in the last 2000 years. Of these, 34 exceeded floods expected to strike once a century (20 would be expected under the old models), and 26 were larger than the so-called 500-year flood (only four of these would be expected under the prevailing models). Two of the floods were monsters that exceeded the design standards of the dam, even with the enhancements added after 1983.

At the other extreme of dismal news is the ongoing drought, 13 years and counting. The lake is hovering around 50% of capacity, and is expected to rise only modestly this year despite good snow conditions in the Rocky Mountains. We may be at the point where we are depending on the occasional El Nino event just to maintain a usable amount of water in the reservoir. There are some who think the reservoir will never have enough runoff to ever fill again.

All in all, this calls into question the wisdom of trying to control such a variable and unpredictable river. And we haven't even dealt with the question of sediment infill. The giant mega-dams are filling with silt at an astounding rate that is shortening their useful life. Ultimately our gigantic engineering projects will give way and the river will once again be in control. It's happened before with gigantic lava flow dams and blockages like Hoover Dam and Glen Canyon Dam will also give way.

Such were my thoughts as I stood on the hilltop overlooking this "mighty work of man". We hit the road again, headed towards Grand Staircase-Escalante National Monument, the largest single park on the Colorado Plateau.

Thanks to Wayne Ranney over at Earthly Musings for the heads up on the recent Colorado River research!

Saturday, June 21, 2014

Tse' bighanilini and Hasdestwazi, "the place where water runs through rocks", and "spiral rock arches."

Glen Canyon was a beautiful, magical place that was unceremoniously flooded under the waters of Lake Powell (and I'm pretty sure John Wesley Powell would have been appalled that his name was given to the lake). Despite the gigantic eyesore of Glen Canyon Dam, there are some incredible places to explore in the immediate vicinity. One of them is Antelope Canyon, one of the Tribal Parks managed by the Navajo Nation. The two parts, upper and lower, of the canyon are called Tse' bighanilini, which means "the place where water runs through rocks", and Hasdestwazi, or "spiral rock arches."
Natural arch within Lower Antelope Canyon
Each of the canyons is worth a look. The upper canyon is justly famous for the noon hour beams of sunlight piercing the near total darkness of the deepest passages. It is also level from one end to the other. But it also requires a ride from town that includes an unbelievable race up a pure stretch of loose dune sand. And it is crowded, especially during the aforementioned noon hours when you might find yourself standing shoulder to shoulder with hundreds of other people. It's not a place for the claustrophobic.
On our recent tour, we opted for the lower canyon. It doesn't have the piercing beams of sunlight, and it is not level, requiring steps and ladders for access. But you don't have to be ferried up Mr. Toad's Wild Ride, and it tends to be far less crowded (in my three trips, anyway).

The tours of these incredibly beautiful works of nature begin beneath the shadow of the monstrous coal burning power plant just outside of Page. The coal mines are sixty miles away, but the energy infrastructure is here near Glen Canyon Dam. We were given a short safety lecture before walking down the end of the lower canyon.
It's hard to believe that such a treasure lies hidden in these folds of crossbedded Navajo Sandstone. The canyon is more than a hundred feet deep in most places, but only a few feet wide at the top. The guide politely asked us not to jump across the top of the canyon, prompting me to wonder what story was behind that rule...
Antelope Canyon drains an area of dozens of square miles, but the rushing waters of the occasional flash floods are forced to cross two ridges of Navajo Sandstone. The rock is cemented well enough to form vertical cliffs, but at the same time the sandstone is easily and quickly eroded by fast-moving sediment rich water. The result is an incredible labyrinth of looping and curving channels.
The natural curves of the canyon are accentuated by the crossbedding of the Navajo Sandstone. The Navajo formed as a gigantic sand dune sea that extended from Wyoming and Colorado to Nevada and eastern California. The crossbeds are the preserved slipfaces of the sand dunes. The dunes were present during the Jurassic Period, when dinosaurs wandered across what is now the southwest United States.
The narrow canyon can be dangerous. Storms that are dumping floodwaters upstream might not be visible from the parking lots. After a horrific tragedy in 1997 that caused the deaths of eleven people, rescue measures have been put into place, and tours aren't offered when rain threatens the headwaters region.
The canyon is full of abstract shapes and forms, and a photographer could wander for hours through the passageways (two hours to be exact, for an extra fee). Photography is allowed and encouraged by the guides, and they offer advice on shutter speeds and the like. It's been said that one can't take a bad picture here, but believe me, it's more than possible! The sharp contrast between light and dark wreaks havoc with photo framing. It challenging, but wonderful fun as well.
My favorite pictures occur where the sunlight is indirect and reflecting from above. The resulting yellow and golden hues are beautiful; the rocks seem to glow with inner light.
The texture and light are unique. If you are ever in Page, don't be afraid to put out the tour cost (between $20-35, with a $20 premium for those noontime tours in the upper canyon).
As is usual with my visits to the canyon, I have more pictures then I have words. Enjoy!

For the second time in my three tours through the lower canyon, our guide offered some beautiful flute music in the deepest part of the canyon. Here's the video:

Then it was time to go. We climbed up the last ladder into the blinding sunlight.

Friday, June 20, 2014

A Rock Outcrop, a River, and Sand flow into a Point Bar...

And the bartender said "is this some kind of joke?"
But it's not a joke of course, it's a simply stunning example of what happens when water flows over stone for a long time. What you are seeing here Horseshoe Bend on the Colorado River a few miles downstream of Glen Canyon Dam and Lake Powell outside of Page, Arizona.

A point bar is a real thing with rivers. When a river loops back and forth as a series of meanders, point bars form as sand ridges develop on the inside of the loop where the water flows more slowly. In the most technical sense, the sand bars in the picture above can be consider an example of the feature, although they are more familiar where rivers are flowing in flat floodplain.

It's obvious that Horseshoe Bend is no longer a flat floodplain! It may have been one at one time, but uplift of the Colorado Plateau (or the subsidence of the lands around the edge of the plateau) caused the river to speed up and start to erode downwards, forming an entrenched meander.
The approach to Horseshoe Bend is a sandy trail about three-quarters of a mile up from a parking lot about five miles south of Page on Highway 89. Although views are wide-ranging along the trail, there is barely a hint of the incredible view that awaits when one arrives at the brink of the cliff and looks down nearly a thousand feet to the river. Stunning is the only word for it.

My old camera couldn't show the entirety of Horseshoe Bend, so I was thrilled I was able to get these wider angle pictures with my new one. It's almost like looking at a petrified rainbow, although it should be said, this view is not entirely natural.

When Glen Canyon Dam was completed in the 1960s, the river was changed forever in terms of a human lifetime. Instead of the normal red silt-laden water, the river flows clear and cold (almost refrigerator cold, about 46 degrees; I can attest to this as I almost drowned in the river last year). As a result, green algae grows in the unnaturally blue river. It's beautiful to look at, but is kind of sad to consider what it should have been. Many of the native species of river life are in decline and cold-loving invasive species are thriving.

A trip-planning note just in case you are headed out to the region this summer: Highway 89 between Bitter Springs and Page was closed down by a serious slope failure along the Echo Cliffs Monocline. It may be years, if ever, before the highway will be repaired. In the meantime, the Arizona Department of Transportation has constructed a newly paved highway replacing Navajo Route 20. Although the detour is supposed to be temporary, I suspect it is permanent despite any feelings of the Navajo Nation about a new busy highway in a formerly isolated part of the reservation. There are far fewer engineering problems where the new highway crosses the monocline.

Wednesday, June 18, 2014

How Did the Grand Canyon Happen? It's a Mystery, a Delightful Mystery!

And that's something that I really love about science and geology: the acknowledgement that there are things we don't know...yet. No matter how ingenious our technology becomes, no matter how much data we collect, there will always be new things to discover, and each week research reveals something new about our Universe that no one has ever known before. And that's the fun of exploring a wonder like the Grand Canyon. We don't completely understand why it's there!

There are many things we can say about how the Grand Canyon formed. For instance, the Colorado River carved the Grand Canyon. That's an answer that satisfies many, because the river is big, drains a large region, and lies at the bottom of the present-day canyon. It carries millions of tons of silt and sand downstream for temporary storage in Lake Mead before it ends up in the Gulf of California. The canyon is getting a tiny bit deeper and wider each and every day. That much is clear.
The first problem is a big one: how did the Colorado River get over the Kaibab Plateau (above)? The Kaibab tops out at over 8,000 feet, but the lands east from which the Colorado flows are 3,000 feet lower. The easy answer is that the river was there and the land rose around it while the river cut down, keeping pace with the uplift. That is an appropriate hypothesis, but unfortunately can't be true because the plateau is 70 million years old while the Colorado River cannot have exited the plateau at the present Grand Wash Cliffs locale prior to 16 million years ago. The main lesson of several different possible explanations is that there has not always been a single through-going Colorado River. There have been several river systems that were later integrated into a single river.
So which of those Colorado Rivers was it that carved the Grand Canyon? Was it the Colorado River we see today that flows (or once flowed) into the Gulf of California? If that's the case, the Grand Canyon can be no more than 4-6 million years old, because that's when the Gulf of California opened up. Was it the "Colorado River" that carved these entrenched meanders near Peach Springs (photo below)? If it was, then we are talking about a river that carved a 4,000 foot deep canyon more than 50 million years ago. A river that flowed northeast, almost opposite of what the Colorado River does today.
Or was it this river (below)? Looking at the shape of the tributary streams, it looks like this river is flowing northeast...but it's not. That's Marble Canyon, occupied by the Colorado River just downstream of Lees Ferry, and just upstream of the Grand Canyon itself. The river flows southwest, but the topography is strongly suggestive of a river that once flowed in exactly the opposite direction.
How in the world can a river completely change direction? It seems to fly in the face of physics and the laws of gravity. But there are ways that it can happen and we don't have to break the law (of nature). One of them is called stream piracy, and it is happening even today on the Colorado Plateau, at another familiar national park, Bryce Canyon.

The gradient of a river is the relative slope of the river, the altitude it drops over a given distance along the riverbed. Higher gradient streams flow faster, and therefore tend to have greater erosive capacity. Since the highest gradients are often at the headwaters of a stream, erosion often acts to eat away at the edge of the drainage or plateau where the river originates. This upstream lengthening of the river is called headward erosion.

Check out the Google Earth image below of Bryce Canyon National Park. The famous hoodoos, or spires, form at the edge of the plateau and are light orange in color. The erosional amphitheaters represent the headwaters of the Paria River and other tributaries to the Colorado River. The amphitheaters completely surround a second north-flowing drainage, the East Fork of the Sevier River. The headwaters are carving away at the plateau edge, getting closer and closer to the channel of the Sevier River. In the near geologic future, the water that flows north towards Salt Lake City will instead flow southwest towards Las Vegas. Early settlers in the region took advantage of the impending piracy; they dug a canal that diverts some of the Sevier River into the Paria River drainage to support agricultural fields downstream.
The picture below highlights the edge of the plateau and the two drainages. Ultimately it is tectonic activity (raising or sinking of the crust) that determines the response of river channels. And there have been many tectonic changes in and around the Colorado Plateau where the Grand Canyon was eroded.
How are we to make sense of these discrepant pieces of data? In essence, it is the discrepancies that lead us to better understand how the Grand Canyon might have happened. While we don't have a full story to explain the development of the canyon, there are certain things we do know (this information is summarized nicely in Wayne Ranney's excellent book Carving Grand Canyon: Evidence, Theories and Mystery, published by the Grand Canyon Association).
From 80 to 30 million years, river in the Colorado Plateau region flowed northeast into large inland lakes. The Claron Formation, which forms the hoodoos of Bryce Canyon, was one of these lake systems. The highlands from which the rivers flowed originated in the compressional tectonics of the Laramide Orogeny.

From 30 to 16 million years there was a dark period for which there is little evidence revealing the type of river activity. According to Ranney, the drainages became ponded, dry, rerouted, reversed, or "confused".

From 16 to 6 million years, basin and range style faulting severely disrupted the landscape, creating deep sedimentary basins that were isolated from one another. The sinking of these basins may have formed the high gradients that initiated deep canyon cutting, but until 6 million years ago, no Colorado River flowed of the Colorado Plateau at any particular point with any relationship to today's course.

Between 6 and 4 million years ago, the opening of the Gulf of California caused the integration of different river drainages into the unified Colorado River we know and love today. Much of the cutting of the Grand Canyon probably took place during this time period, aided in large part by extremely high river discharges fed by melting glaciers in the Rocky Mountains during the last ice age. 
What we can say is that the Grand Canyon and the Colorado River exist today, and the canyon continues to be carved and excavated by the river. We are lucky to have evolved just in time to see the canyon, because in a geologically short period of time, the entire plateau can be expected to erode away, removing nearly two billion years of geological evidence. It's true that other canyons will form, but it's hard to imagine any place as grand as this one. Get out and see it while you can!