Introduction
Although the Sierra Nevada is relatively young, its surface uplift and exhumation
history is not well known. Until the past decade or so, it was believed that
the present relief of the Sierra Nevada had only existed for about 10 Ma. For
example, Unruh (1991) argues that tilted sedimentary strata in the Great Basin
on the western side of the Sierra Nevada indicate late Cenozoic rock uplift,
assuming that the tilting of the sedimentary units records the tilting (and
therefore uplift) of the Sierra. Other studies, however, infer that elevations
of the Sierra Nevada have been as high as present-day elevations for 20 Ma or
more (Wernicke et al., 1996) and may have actually decreased in the last 10
Ma (Small and Anderson, 1995). Studies of oxygen isotope compositions on the
eastern flank of the Sierra Nevada by Chamberlain and Poage (2000) and Poage
and Chamberlain (2002) indicate the latter; their results, discussed in the
Sierra Nevada section below, suggest that the present
relief of the Sierra Nevada has existed for at least 16 Ma.
Paleoelevations of the Rocky Mountains are also poorly constrained. One group of studies suggests the relief of the Rockies increased in the Miocene (i.e., Burchfiel et al., 1992), and another group of studies indicates high relief in Wyoming throughout the Cenozoic (i.e., Wolfe et al., 1998; Dettman and Lohmann, 2000). Studies by Norris et al. (1996) and Morrill and Koch (2002), discussed below in the Rocky Mountains section, use oxygen isotopes to assess the possibility of snowmelt from and therefore paleoelevations of the topography surrounding the Green River Basin. Norris et al. (1996) find an oxygen isotope signal, indicating that high topography surrounded the Green River basin. Morrill and Koch (2002) argue that this signal could indicate diagenetic alteration, rather than high topography.
Paleoelevation of the Sierra Nevada
Paleoelevation of the Rocky Mountains
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