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Geologic Investigation Series I–2667
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Correlation of Jurassic San Rafael Group and related rocks from Blanding, Utah, to Dove Creek, Colorado

By Robert B. O'Sullivan

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The Middle Jurassic San Rafael Group consists of sandstone, siltstone, and shale. In the study area, the San Rafael Group is mostly concealed beneath younger rocks but does crop out along Comb Ridge and in the canyon of the Dolores River in the western and eastern parts of the study area respectively. In an intervening area along Montezuma Creek, the upper part of the San Rafael Group crops out for about 10 mi; at one locality all of the group is exposed.

In the study area, two unconformities are associated with the rocks described herein. The unconformities separate the San Rafael Group from the underlying Lower Jurassic Navajo Sandstone and the overlying Upper Jurassic Morrison Formation. The unconformities— termed J-2 at the base of the San Rafael and J-5 at the top—are also recognized throughout much of the Western Interior of the United States (Pipiringos and O’Sullivan, 1978). The J-5 unconformity is the datum used to construct the line of graphic sections and the restored stratigraphic diagram of this report.

Version 1.0

Posted November 1998

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