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The Paris-Willard thrust trends in a north-south direction parallel with the eastern edge of the Bear Lake plateau of north-central Utah and southeastern Idaho. In places along the leading edge of the thrust, formations as old as the Cambrian Brigham Quartzite have overridden the Jurassic Nugget Sandstone and various Triassic formations. Movement on the Paris-Willard thrust began in latest Jurassic or earliest Cretaceous time, displacing rocks from the west to the east over 10 mi (16 km).
Seismic surveys indicate that from the leading edge to approximately 6 mi (10 km) west, the Paris-Willard thrust is relatively thin skinned. Detailed structural cross sections suggest that shales in the Triassic Woodside or Ankareh Formations, acted as "sled runners" for Cambrian quartzites moving on the overlying Paris-Willard plate. The thickness of this overlying thrust plate is believed to range between 3,000 and 8,000 ft (900 and 2,400 m), with a complete Paleozoic section present on the underlying Crawford thrust plate. With the exception of two wells drilled on the edge of the Paris-Willard thrust, 600 mi2 (1,500 km2) of potential Paleozoic reservoirs beneath the thrust have never been tested. Seismic interpretations indicate the presence of several large tructures in the sub-thrust where formations such as the Phosphoria (which tested gas on the Crawford plate at Hogback Ridge field to the east), Weber, and Madison would be the primary objectives. Recent studies by several workers suggest units in the Phosphoria and other Paleozoic formations are excellent potential source rocks.
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