Tertiary normal faulting in the Canyon Range, eastern Sevier Desert

The contact between pre-Mesozoic and Tertiary rocks in the western Canyon R ange, west-central Utah, has been interpreted as a large, low-angle normal fault that marks the breakaway zone of the hypothesized, basin-forming Sevi er Desert detachment. Recent fieldwork suggests that the contact may in fac t be depositional along much or all of its length. Deformational fabric in the supposed footwall likely traces to the Mesozoic Sevier orogeny rather t han to Tertiary detachment faulting. Kinematic indicators at the range fron t are not generally consistent with low-angle normal-fault motion; instead, well-exposed high-angle faults are the dominant range-bounding structures. The Tertiary conglomerates of the western Canyon Range foothills, previous ly viewed as an evolving syntectonic deposit related to detachment faulting , are here reinterpreted as three distinct units that reflect different per iods and tectonic settings. The pattern in these conglomerates, and in faul t-offset gravity-slide deposits that mantle the western foothills, is consi stent with block faulting and rotation along several generations of high-an gle structures. Local seismic-reflection data lend qualitative support to t his interpretation, and underscore the need to consider alternative working hypotheses for evolution of the Sevier Desert basin.