The Colorado Plateau presents a contrast between deep and seemingly recent erosion and apparently only mild late Cenozoic tectonic activity.
Researchers have recently proposed multiple sources of epeirogenic uplift and intriguing patterns of differential incision, yet little or no
quantitative constraints exist in the heart of the plateau to test these ideas. Here, we use both optically stimulated luminescence (OSL) and
uranium-series dating to delimit the record of fl uvial strath terraces at Crystal Geyser in southeastern Utah, where the Little Grand Wash fault
crosses the Green River in the broad Mancos Shale badlands of the central plateau. Results indicate there has been no deformation of terraces
or surface rupture of the fault in the past 100 k.y. The Green River, on the other hand, has incised at a relatively rapid pace of 45 cm/k.y. (450
m/m.y.) over that same time, following a regional pattern of focused incision in the “bull’s-eye” of the central plateau. The Little Grand Wash
fault may have initiated during Early Tertiary Laramide tectonism, but it contrasts with related structures of the ancestral Paradox Basin that are
presently active due to salt dissolution and focused differential erosion. We also hypothesize there may be a Pliocene component of fault slip
in the region linked to broad-wavelength erosional unloading, domal rebound, and extension. An apparent rapid decrease in incision rates just
upstream through Desolation Canyon suggests the Green River here may have recently experienced an upstream-migrating wave of incision.
- rapid river incision
- inactive fault
- central Colorado Plateau
- patterns of erosion