Evaluating the role of topographic inversion in the formation of the Stanislaus Table Mountains in the Sierra Nevada (California, USA)

Abstract

The Table Mountains, a flat-topped series of ridges capped by a 10.4 Ma latite flow in the Stanislaus River watershed, are considered to be evidence for late Cenozoic uplift-driven landscape rejuvenation in the northern Sierra Nevada range (California, USA). The commonly accepted theory for the formation of these mesas posits that the latite flowed and cooled within a bedrock paleovalley and, since then, the surrounding landscape has eroded away, leaving behind the volcanic deposit as a ridge. Although this theory is accepted by many, it has not been thoroughly tested. In this study, I examine a series of geological cross-sections extracted along the length of the latite deposit to determine whether the evidence supports the existence of bedrock valley walls on both sides of the 10.4 Ma flow. I find that the presence of older Cenozoic deposits adjacent to the latite flow precludes the possibility that the flow would have been constrained within a bedrock valley. Moreover, the cross-section from an 1865 report that has been offered as evidence of topographic inversion (and subsequently reproduced in numerous publications) does not accurately represent the topography at that site. I conclude that there is no evidence that the bedrock topography has been inverted and that instead, the latite flowed within a channel cut into underlying Cenozoic deposits, which have since mostly eroded away. This study, therefore, refutes the hypothesis that the Stanislaus River watershed was rejuvenated in the late Cenozoic and challenges the claim for recent significant uplift of the region.