The contact between pre‐Mesozoic and Tertiary rocks in the western Canyon Range, west‐central Utah, has been interpreted as a large, low‐angle normal fault that marks the breakaway zone of the hypothesized, basin‐forming Sevier Desert detachment. Recent fieldwork suggests that the contact may in fact be depositional along much or all of its length. Deformational fabric in the supposed footwall likely traces to the Mesozoic Sevier orogeny rather than to Tertiary detachment faulting. Kinematic indicators at the range front 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, previously viewed as an evolving syntectonic deposit related to detachment faulting, are here reinterpreted as three distinct units that reflect different periods and tectonic settings. The pattern in these conglomerates, and in fault‐offset gravity‐slide deposits that mantle the western foothills, is consistent with block faulting and rotation along several generations of high‐angle structures. Local seismic‐reflection data lend qualitative support to this interpretation, and underscore the need to consider alternative working hypotheses for evolution of the Sevier Desert basin.

中文翻译：

---

东塞维尔沙漠峡谷山脉中的第三纪正断层

犹他州中西部峡谷山脉西部的前中生代岩石和第三纪岩石之间的接触被解释为一个大的、低角度的正断层，标志着假设的、形成盆地的塞维尔沙漠拆离带的分离带。最近的实地工作表明，接触实际上可能是沿其大部分或全部长度的沉积。假定的下盘中的变形构造可能追溯到中生代塞维尔造山运动，而不是第三纪拆离断层。范围前沿的运动学指标与低角度正断层运动普遍不一致；相反，暴露良好的高角度断层是主要的范围边界结构。峡谷山脉西部山麓的第三纪砾岩，以前被视为与拆离断层相关的演化同构造沉积物，在这里被重新解释为三个不同的单元，反映了不同的时期和构造环境。这些砾岩以及覆盖西部山麓的断层偏移重力滑坡沉积物的模式与沿几代高角度构造的块断层和旋转一致。当地地震反射数据为这种解释提供了定性支持，并强调需要考虑塞维尔沙漠盆地演化的替代工作假设。