Seminar – The (Real) Geologic History of the Stanislaus Table Mountains and Yosemite Valley

Dr. Manny Gabet | San Jose State University

Presenting: "The (Real) Geologic History of the Stanislaus Table Mountains and Yosemite Valley"

Hosted by: Geological Oceanography Lab

MLML Seminar | September 30th, 2025 at 4pm (PDT)

Watch the Live Stream here or here

The (Real) Geologic History of the Stanislaus Table Mountains and Yosemite Valley

In 1865, J.D. Whitney published a hypothesis, originally proposed by his colleague Ian Brewer, that the Stanislaus Table Mountains were a form of ‘inverted topography.’ According to this theory, a 10-million year old lava flow had travelled down a mountain canyon and solidified along the river bed. Over time, the adjacent valley walls had eroded down, transforming the lava-capped river bed into a series of ridges that are now recognized as the table mountains. Furthermore, Whitney reasoned that this much erosion could only have been accomplished as a result of tilting and uplift of the Sierra Nevada. Whitney’s explanation was the genesis for the dominant theory that the Sierra Nevada is a relatively young range, having popped up only in the past 5-10 million years. Similarly, the initial formation of Yosemite Valley has also been attributed to recent uplift. In my talk, I will present evidence demonstrating that the Stanislaus River watershed has not undergone any dramatic transformations and that, instead, it looks very much like it did 30-40 million years ago. In addition, I will present evidence showing that Yosemite Valley was initially cut by a river draining a large volcanic plain that once buried the crest of the northern Sierra. Both of these studies, as well as others, contribute to a growing body of evidence that the Sierra Nevada is an ancient range, rising up at least ~40 million years ago.

Dr. Manny Gabet

I’m a geomorphologist, which means I study how landscapes evolve over time. Some of my past research has focused on erosion in the Himalayas, the role of fires in triggering debris flows in Montana, and the mechanics of landslides. More recently, I’ve been investigating the geologic history of the Sierra Nevada over the past 40 million years and have been discovering that the dominant theory on the age of the mountain range is not supported by the evidence.