Structures that were active in the Jurassic, inferred from isopleth and structure contour maps, significantly affected depositional patterns in the Westwater Canyon Member of the Morrison Formation in the southern

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San Juan basin, northwestern New Mexico. Isopleth maps illustrate geometry of the major depositional units, distribution of sandstone depo-centers, and large-scale lithofacies variations within the units. A reconstruction of topography at the base of the Westwater Canyon Member shows a series of subparallel paleotopographic lows and highs that trend east-southeast. The Westwater Canyon is thick and sandy along paleotopographic lows, but is thin and less sandy over the paleogeographic highs. These relationships suggest active structural control of sedimentary facies along east-southeast-oriented folds or faults by differential subsidence during deposition of the unit. Locally, east-southeast-oriented basement faults that were episodically reactivated since the Precambrian may be detect d by detailed seismic reflection studies.

Depositional patterns and lithofacies distribution, in turn, appear to have controlled the location of uranium deposits. Primary and remnant uranium ore in the Westwater Canyon is restricted to east-southeast-trending depocenters defined by anomalously thick and sandy facies with relatively high sandstone:mudstone ratios. Redistributed ore is also localized in anomalously thick zones of the Westwater Canyon with relatively low sandstone:mudstone ratios.

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