Cain City quadrangle is south of the Llano region and is in the marginal portion of the Edwards Plateau where much of the plateau surface has been destroyed by erosion. Northeastward-trending lobes and outliers of the Edwards Plateau are present in the southern part. The rest of the quadrangle is in the gently undulating broad Pedernales River basin.

The geology of the Cain City quadrangle is shown on a planimetric map since the only topographic map available is the reconnaissance 30-minute Fredericksburg quadrangle. Elevations ranging between 1,512 and 1,932 feet were determined during traversing for control, but neither the highest nor the lowest elevation was reached. However, from the traverse it is estimated that the relief within the quadrangle is about 500 feet, ranging between about 1,500 and 2,000 feet in elevation.

The quadrangle is entirely within the Pedernales River drainage basin and is mostly drained by South Grape Creek, Meusebach Creek, and numerous short branches of Pedernales River. Barons Creek and Palo Alto Creek empty into Pedernales River within the quadrangle.

The Cain City quadrangle is on the southern side of the Llano uplift, and rocks of Ordovician age outcrop as inliers surrounded by Cretaceous rocks. The faulting accompanying the Ouachita orogeny (Barnes, 1948) is not exposed but southeastward dips up to 8� are present in the Paleozoic rocks. The Cretaceous rocks are essentially horizontal, dipping mostly southward about 8 feet per mile. A gentle nose with a southeastward trend is present, and one of the few faults in Cretaceous rocks noted in the vicinity of the Llano uplift is in the southern part of the quadrangle.

Broader discussions of the stratigraphic, structural, economic, and geophysical problems of the region cannot be given in the space available. References cited below deal with some of these problems. This publication on the Cain City quadrangle is one of a series of similar publications, an index to which is shown on the opposite page. The reader is referred to this index map to locate other quadrangles mentioned in the present text.