The Middle Jurassic San Rafael Group and the Upper Jurassic Morrison Formation consist mainly of sandstone, siltstone, and shale. The San Rafael Group is widely displayed around Bluff (fig. 1) in the southern part of the study area and along Harts Draw and Dry Valley in the northern part. Along Montezuma Canyon, which is almost 1,500 ft deep, the upper part of the group crops out for about 10 mi; at one locality (sec. 13, fig. 1) all of it is exposed. Elsewhere in the study area, younger rocks conceal the San Rafael Group. The Morrison Formation is also generally well exposed throughout the area. From near Monticello to Harts Draw, Cretaceous rocks conceal the Morrison Formation. In the study area, two unconformities are associated with the rocks described herein. One at the base of the San Rafael Group (termed J-2) at the contact with the Lower Jurassic Navajo Sandstone and the other at the top (J-5) at the contact with the overlying Morrison Formation. The J-5 unconformity is the datum used to construct the line of graphic sections and the restored stratigraphic diagram of this report. The locations of drill holes and measured sections are given in table 1.
