fourth day on the Colorado River, we pulled into camp at Little Nankoweap Creek. The camp was in a beautiful location (as nearly all of our camps were), but as I selected a campsite, my attention was captured by an oddity. There was a huge splash of reddish brown mud laid across the sandy campsite like the edge of a lava flow. What was going on?
Flash floods and debris flows are the tools that erosion uses to deepen tributary canyons and widen the big canyon as a whole. Rock falls and avalanches choke the bottoms of gulches, and every decade or two a cloudburst sends torrents of water down the creeks, forming a slurry mix of mud and rock capable of transporting gigantic boulders. These masses of boulders get dumped in the Colorado and end up blocking parts of the channel, forming the characteristic pools and rapids. The spring floods that once surged through the big canyon would ferry the boulders downstream or grind them into sand and silt, and in this way, the Grand Canyon took shape.
We headed back to camp for a delicious meal of fish tacos, and hit the sack.
Tamarisk trees (also called salt cedar) are found all over the American southwest along river courses, but they aren't a native species. They come out of Eurasia, and having no natural enemies in their American environments, they have proliferated to the detriment of practically all competing species. They concentrate salt on their leaves which ends up in the soil, preventing the growth of other plants. They tend to form impenetrable thickets on river floodplains. They don't offer much in the way of food or shelter to most native species, and with deep taproots, they tend to transpirate vast amounts of precious groundwater into the atmosphere (some estimates put the water loss at 2 to 4.5 million acre feet per year across the southwest, enough to meet the needs of 20 million people, or to irrigate 1,000,000 acres). Some desert rivers stopped flowing on the surface after being invaded by the tree.
I had noticed when we left Lee's Ferry that some of the tamarisks were looking a bit yellow (below), but didn't give much thought to it. It turns out that the Tamarisk Beetle loves tamarisk leaves and nothing else. After years of testing, the (also non-native) beetles were released into the wild, and they began an effective campaign of slowing the growth and spread of the tamarisk in the wild. And unlike some other such experiments, the bugs didn't start eating other native species. It is a reasonable hope that the bugs might one day lead to control (but probably never eradication) of the tree.