The last three reservoirs that I have been to lately have all told the same story with the lack of water. It’s so obvious that the water levels are lower because the areas where the water had been is much lighter in color than the area above the water level line — 20, 30, and more — years ago. It is easy to see this in pictures of Mono Lake, Lake Casitas, and Lake Mead. All very scary sad. I haven’t found any explanation on why the rock faces that were underwater are now very light in color. When looking at natural areas where there were once rivers, lakes; for example, on canyon walls, the color is not so washed out. So, I guess this is caused by mineral deposits from the water? During the Hoover Dam Power Plant tour, the guide pointed out seepage in a rock wall. The seepage causes calcium carbonate deposits and the rock faces where this occurs are lighter in color.
Here’s a PDF about managing seepage in dams. It is 166 pages, so I’m not sure if I’ll get to reading it any time soon.
Okay, and here’s one last picture. It isn’t really related to the color of canyon walls, but… It’s the number 6 turbine on the Nevada-side of the power plant. They have an overhead crane that they use to lift the turbine out of the housing so they can perform maintenance on it.