There were three major glacier periods in the Yosemite area and the last retreated from the Valley about 18,000 years ago. (We still have 2 glaciers – Mt. Lyell and Mt. Maclure.)
The classic “U” shape of glacial carved valleys is not readily evident in Yosemite Valley, because research has shown that the bedrock lies about 2,000 feet below today’s roads. How did that happen? During its time, the last glacier slowly covered down to the area between El Capitan and Bridalveil Fall. As it dug deep, stone and debris was deposited in front of it. A terminal morain. When it finally melted and retreated back to the east, the terminal moraine created an earthen dam. The dam stopped the waters from the melting ice and created a lake, geologists call it “Yosemite Lake.” By 10,000 years ago the lake had filled with sediment disguising the U shape.
Scientists believe the “U” shape is still there – only it’s 2,000 feet below the surface. Galen Clark, the first guardian of the park, was bothered by all the mosquitos in the swampy remains, so he dynamited the berm away to drain what remained in the late 1800’s. You can still slightly notice the berm as you enter Southside drive before Bridalveil Fall.
Here is an excellent rendering of Yosemite Lake might have looked like by Rory Beyer, a Junior Guide this season with Lasting Adventures, Inc., a premier Guide Service based in Groveland.
Unrelated thought worth quoting: “You took my doubts, you took my fears.
You led me through this lake of tears. So close we are, but still apart, not in mine, but in your heart.” – L’Ame Immortelle
MrHalfDome™ – Rick Deutsch – www.HikeHalfDome.com