Water in a Dry Land: Joshua Tree National Park, and why Twentynine Palms is missing a few

It is, of course, a cliche to say that water is life. I can barely imagine a more terrifying thought than to be trapped in the open in a place like the Pinto Basin in Joshua Tree National Park (above) on a scorching hot summer day without a car, without a phone (no coverage anyway), and without water. The Pinto Basin is the rarely visited wilderness end of Joshua Tree National Park, a place far removed from the famous granite boulders of Wonderland of Rocks or Hidden Valley. The Pinto Basin is a vast alluvial plain crossed by two old dirt tracks leading to abandoned mines, and nothing else.

The Pinto Basin was never developed like other desert basins in California because of a lack of available water resources and the arrival of the Great Depression just as speculators were moving into the region. The establishment of the monument sealed the deal and protected the wide basin from any more development.

It wasn't always like this. Studies at Joshua Tree have established that the region was more tropical for millions of years, and that during the Ice Ages a stream flowed through the valley. It was a place where humans could thrive instead of simply surviving. Archaeological work has established the presence of a people (the Pinto Culture) that lived in the basin from around 9,000 to 2,000 years ago.
Water is precious in the desert, and there are precious few sources there today. Ironically, the source of the water that is there is the same as the water the Pinto People used thousands of years ago. The gravels of desert basins like the Pinto act like giant sponges, storing water in the spaces between sand grains in the thousands of feet of loose sediment filling the valleys. Billions of gallons of Ice Age water remain hidden deep in the sediments, revealed only when geological conditions force water to the surface.

California has her faults, and faults are one of the ways that water can be forced to the surface. The grinding along fault zones produces a clay-like material called gouge, which is impermeable to water. Water flowing slowly underground can be dammed by fault gouge and forced to the surface. I visited two of those spots last week.

The first is Cottonwood Springs at the less-visited south end of the park (picture above). Water still flows there, but only a trickle. During the mining era, some 3,000 gallons a day provided the only secure water source for many miles around. The palms were planted in the 1920s (though they are a native species). The cottonwoods were present earlier. Water has been present here for thousands of years, indicated not only by Native American grinding holes in the rock, but also from travertine-like rocks in the area, deposited by water over tens of thousands of years. Needless to say (but I always say such things anyway), the water attracts a wide variety of animal and insect life.

The second "spring" we visited was the Oasis of Mara in an outlier of the park that serves as park headquarters in Twentynine Palms. Early miners called the oasis "Twentynine Palms Oasis", but the present name is a derivation of the Native American name for the spot. The oasis is marked by a line of fan palms along a recently formed scarp formed by the active Pinto Mountain fault (visible in the picture above). I was fascinated by the beautiful little pond in the midst of the healthiest looking fan palms, but I soon realized it was lined with plastic. A bit of research (like reading signs on the nature trail!) revealed that the springs of the Oasis of Mara have been dry for decades. It's not too hard to figure out why. The presence of water led to the establishment of the town of Twentynine Palms, and the town residents started drilling wells right away, drawing down the groundwater table and and drying up the springs. I'm not sure there are actually 29 living palms left today.

The last source of water we saw was a lake, of all things, hidden among the granite boulders. That's a unique Joshua Tree story for another post.

I've used three sources of information about the park beyond my own observations:

Cates, Robert, 1995, Joshua Tree National Park: A Visitor's Guide, Live Oak Press, 100 pages.

Trent, D. and Hazlett, R., 2002, Joshua Tree National Park Geology, Joshua Tree National Park Association, 64 pages.

Eggers, M, editor, 2004, Mining History and Geology of National Park, San Diego Association of Geologists, c/o Sunbelt Publications, 119 pages.

Taking Granite for Granted? Looking at Gneiss Rocks in Joshua Tree

Where can one find the oldest rocks in California? And for that matter, any place west of Utah and Wyoming? Some well-seasoned geological travelers would point to the bottom of the Grand Canyon, where dark metamorphic gness and schist lie exposed below the Great Unconformity. Others might point to the Black Mountains in Death Valley National Park, where similar rocks are exposed along the unique turtleback faults of the deep graben that forms the main axis of the park. These beautiful rocks formed during a collisional event (really two) between 1.65-1.75 billion years ago that formed a huge mountain range that extended across the southern part of the North American continent for an unknown distance westward. At the time, most of the continents of the world were combined into a supercontinent called Rodinia (which existed prior to the better-known Pangea).
If one takes granite for granted, as I did once at Joshua Tree National Park, one might miss one of the unexpected pleasures of exploring the park. The giant granite boulders in the Wonderland of Rocks may catch most of the attention, but there are secrets in the somewhat bland looking hills in the south and central parts of the park: the oldest rocks in the state! The Pinto gneiss and related rocks in Joshua Tree are related to those seen at Grand Canyon and Death Valley. These are the ancient metamorphic rocks that the granitic magmas invaded. These rocks once may have been sands on a beach some 2 billion years ago, or muds on a sea floor. Some may have been volcanic flows. All have been baked by the molten rock and squeezed into their present shape.
South of Cottonwood Springs at the less-used park entrance near Chiriaco Summit out of Indio, a desert gully along the park road exposes the contact zone between the granite and the gneiss (pronounced 'nice'). The contact is marked by an intrusion breccia, bits and pieces of the metamorphic rocks enveloped in the granitic rock. The isolated chunks of metamorphic rock are called xenoliths ('alien rock').
A hike to the Mastodon Mine out of Cottonwood Springs reveals one of the most unique exposures of xenoliths (or enclaves, see comments below) that I have ever come across. The metamorphic rocks are weathering differently than the granitic rock, and end up protruding like chocolate chips in cookie dough!
Joshua Tree National Park is a fascinating treasure. The story shall continue....