Sunday, October 9, 2011
Fall in the Sierra Foothills
Still, it did rain last week, so the air was cooler today, and there was a freshness we haven't felt in months. We took a little picnic this afternoon up the Tuolumne River into the Sierra Nevada foothills. We stopped at Old Basso Bridge, a river crossing that was once the focus of some rather intense gold dredging. Numerous ponds from the mining days dot the landscape, filled with groundwater. Today they provide habitat for wildlife, and a nice recreational area for fishing and wildlife photography.
The other interesting sight at the park are the boulders they've used for rip rap to reinforce the base of the bridge. They are chunks of a deeply oxidized conglomerate that is found locally in a layer called the Ione formation. It formed in Paleogene time as rivers flowed over the not-quite risen Sierra Nevada. The rivers had their source in central Nevada or more distant regions, and flowed through a landscape much different than that of today.
The rivers ended in an estuary/delta complex along the Pacific Ocean (the Central Valley was a shallow sea at the time), and in a series of swamplands that later produced lignite coal that was utilized during the settlement of California after the Gold Rush. Fossils of palms and other warm weather vegetation indicate tropical conditions.
Fall is just beginning. I'm looking forward to some color (of the leafy kind) in the next few weeks!