A striking 50 mile long ridge, Stanislaus Table Mountain was once a river valley – the ancestral Stanislaus River to be exact. Here is the story:
Between 6-26 million years ago volcanoes in the Sierra Mountains of California were spewing out lava and huge amounts of ash on the western slopes. The Sierras were also rising and rivers cut deep channels into these volcanic sediments.
About 9 million years ago, one huge lava flow traveled from the present day Sonora Pass area, downslope about 50 miles. It went far beyond any of the other volcanics by following the river valley of the ancient Stanislaus River. The flow ended near present day Knights Ferry.
In the ensuing 9 million years, the lava flow gradually became the highest part of the landscape as the softer sediments around it were removed. Today, the lava that once filled the lowest parts of the river channel is instead the highest part of the landscape. This is a classic and very striking example of “inverted topography”. You see it as you drive Highway 108/120 between Knights Ferry and Sonora.
If you like geology related posts check out Geotripper and thanks to it’s author Garry Hayes for some of the information in this article and the lead photo. Here also is a link to a blog post he wrote about hiking to the top of the inverted stream pictured above.
- Geologic History of Middle California (California Natural History Guide #43) Arthur D. Howard. University of California Press. 1979.
- Stanislaus Table Mountain from Above. Gary Hayes. Geotripper website. March 23, 2011.