The late paleobotanist Howard Schorn, retired Collections Manager of fossil plants at the University California Museum of Paleontology, excavates the plant-bearing chocolate shales at Sailor Flat; he was vitally involved in a fascinating geological mystery story: Just how high was the ancestral Sierra Nevada during the geologic past? The traditional view, championed by the late paleobotanist Daniel I. Axelrod and others, is that the Sierra Nevada, as we know it today, is a relatively recent topographic expression, uplifted to its present dramatic elevations mainly during the past five million years--with most of that uplift occurring over the past three million years. But, studies based on rather recent sophisticated geophysical evaluations of mountain ranges, combined with paleobotanical leaf character analysis (study of leaf size, shape, venation, and percentage of entire to serrated margins, among other parameters, to help determine the paleoclimate and paleoelevation of a given fossil site), have suggested quite strongly that the Sierra Nevada, along with the neighboring ancestral Great Basin region, stood just as high if not higher during the geologic past than at present.
Postscript: The conclusion is now concluded, as it were. What's decided, finally, is that the ancestral central to southern Sierra Nevada existed during Eocene times as a moderately low western slope to a high plateau region--the so-called Nevadaplano--that stretched eastward across present-day Nevada, an Eocene upland area that rose as high, if not higher, than the peak elevation seen there today. At around 16 million years ago, the Nevadaplano began to collapse, drop, through extensional geophysical strains associated with incipient formation of the Great Basin, eventually falling to approximately present-day elevations by about 6.8 million years ago.
Which means, ultimately, that the central to southern Sierra has indeed been dramatically uplifted during the past five million years or so. On the other hand, northern Sierran regions have remained at pretty much the same elevations as those that existed during deposition of the Eocene aurifierous gravels some 50 to 40 million years ago. So it turns out that everyone involved in the Sierran elevation studies got it partially correct: the grand solution to the Sierra Nevada Eocene elevation problem turned out to be a major compromise. Axelrod got it mostly right, it turns out--around two-thirds of the Sierran length has indeed been greatly uplifted during the past five million years.