The area described, nearly 1,000 square miles, lies in Eddy and Otero Counties along the south boundary of New Mexico and includes most of the northern part of the Guadalupe Mountains and a considerable area of plains.
Beneath the mapped area, but not exposed on the surface, are rocks ranging in age from Precambrian to Early Permian. Overlying the Precambrian rocks is the Bliss Sandstone of Ordovician age. The Bliss is overlain by the Lower Ordovician El Paso Formation. The El Paso, in turn, is overlain, in the eastern part of the area, by a unit which is tentatively correlated with the Middle Ordovician Simpson Group of Oklahoma. Under much of the report area, however, the El Paso is overlain by the Montoya Dolomite of Late Ordovician age. Above the Montoya is the Fusselman Dolomite of Silurian age, which is overlain by a unit that is tentatively correlated with the Percha Shale of Late Devonian age. Above the Percha (?) is cherty limestone of Mississippian age, which is overlain by a unit correlated with the Upper Mississippian Helms Formation. Pennsylvanian rocks in the report area range in thickness from 0 to more than 4,000 feet. Both the lithology and thickness of the Pennsylvanian rocks were influenced by Pennsylvanian tectonic movements within the area and are highly variable.
Permian rocks of the area are divided from southeast to northwest into three facies: Delaware basin, basin margin, and Northwest shelf. The basin rocks are mainly confined to the subsurface, whereas the basin-margin and shelf rocks are widely exposed. In the basin, the lowest Permian rocks are referred to the Wolfcamp Series. Next above is the Bone Spring Limestone assigned to the Leonard Series. The Bone Spring is overlain by the Brushy Canyon, Cherry Canyon, and Bell Canyon Formations of the Delaware Mountain Group which is assigned to the Guadalupe Series. Overlying the Delaware Mountain Group is the Castile Formation of the Ochoa Series. A solution breccia which was mapped with the upper part of the Castile Formation probably represents the Salado Formation. This breccia is overlain by the basal part of the Rustler Formation of the Ochoa Series, the youngest Permian formation in the area.
In the basin-margin area, the Wolfcamp Series is represented by a broad transition zone in which rocks of the basin facies grade into all but the uppermost part of the Hueco Limestone of the Northwest-shelf area. The Leonard Series in the basin-margin area is represented by the Victorio Peak Limestone and Cutoff Shale. An unconformity representing Brushy Canyon time separates the Cutoff from the overlying shelfward-projecting sandstone tongue of the Cherry Canyon Formation. This tongue is overlain by the Goat Seep Dolomite which grades basinward into the Cherry Canyon Formation. The Goat Seep is overlain by the Capitan Limestone. The Capitan is subdivided into a massive member and a breccia member which are transitional into one another both laterally and vertically. The breccia member grades southeastward into the Bell Canyon Formation of the Delaware basin.
In the Northwest-shelf area the lowest Permian formation is the Hueco Limestone. Most of the Hueco is equivalent to basin rocks of the Wolfcamp Series, but the uppermost part may be of early Bone Spring age. Overlying the Hueco is the Yeso Formation which is laterally equivalent to most of the Victorio Peak Limestone. Above the Yeso is the San Andres Limestone. The basal part of the San Andres may grade into the uppermost part of the Victorio Peak; part of it grades into the Cutoff Shale. The medial part of the San Andres apparently has no equivalent in the basin-margin area and seems to be equivalent to the Brushy Canyon Formation of the Delaware basin. The uppermost part of the San Andres grades laterally into the sandstone tongue of the Cherry Canyon Formation. Shelf rocks equivalent to the Goat Seep Dolomite are the Grayburg and Queen Formations which are the lower two formations of the