Good to excellent source rocks are present in the Late Proterozoic Chuar Group of northern Arizona. Chuar mudstones contain up to eight percent total organic carbon, average three percent, and are within the principal oil-generating window. Chuar Group strata accumulated in a basin which extended from north-central Arizona into south-central Utah, and possibly into north-central Utah. The southern margin of the basin was influenced by the Mesa Butte fault in northern Arizona. Its eastern margin was influenced by a north-trending fault on the western flank of Monument uplift. Uplift across the area of the Grand Canyon ended deposition in the marine or lacustrine Chuar basin at about 800 Ma. The Chuar Group sub crop extends northward from outcrops in Grand Canyon into south-central Utah. There, the Tidewater Kaibab Gulch Unit #1 well penetrated 1,128 feet of Chuar Group strata. Rollover anticlines, sand pinchouts, and stratigraphic traps may be present in northern Arizona between the Tidewater well and the .. Grand Canyon. In structurally depressed terrane in the Grand Canyon, the Chuar is overlain by the continental Sixtymile Formation. Elsewhere, the Tapeats Sandstone overlies the Chuar Group probably throughout much of the extent of the Chuar subcrop. Oil was reported from the Tapeats Sandstone in the Collins Cobb Navajo #1-X well in Coconino County, Arizona. This oil may have migrated from Chuar Group source rocks. Structural closure on the pre-Cambrian unconformity is mapped east of the Cobb well beneath Kaibito Plateau in northern Arizona.