Precambrian geology of the Van Horn area, Texas
— Donald M. Davidson Jr.

Precambrian rocks are exposed in the Van Horn, Texas area as a result of block faulting of a number of adjacent, but spatially disconnected mountain ranges (fig. 1). The area has been referred to as the Van Horn Dome (King and Flawn, 1953) but can be considered domical only in the sense that it has tended to be a positive structural element during Phanerozoic time.

This domical physiographic structure consists of two distinctive geological terrains of late Precambrian (Proterozoic) age. The southern third of the area is composed of a thick (6000-7000 m) sequence of older, low- to medium-grade metamorphic rocks, while the northern two-thirds contains a thinner (3000 m) assemblage of younger, relatively unmetamorphosed sedimentary and volcanic units.

A major structural discontinuity, the Streeruwitz overthrust, forms the boundary between these two terrains, and movement along this surface presumably placed the older, southern metamorphic rocks over portions of the younger lithologies, locally folding them, at 950 to 1000 m.y. (Denison and Hetherington, 1969).

Erosion and incisement of the area occurred prior to the deposition of a late Precambrian(?) clastic unit some 300 m thick, the Van Horn Sandstone. The region underwent tilting prior to deposition of younger Paleozoic and Mesozoic sedimentary units which, together with the older Precambrian rocks, have been offset by faults of Tertiary age.