Wolfcampian upper Hueco Formation of the Robledo Mountains, Dona Ana County, New Mexico
— David V. LeMone, Ronald D. Simpson, and Karl W. Klement

The Robledo Mountains are located in central Dona Ana County in south-central New Mexico. The mountains are a wedge shaped horst of Paleozoic sedimentary rocks (Lower Ordovician-Lower Permian) and Cenozoic clastic, volcanic, and intrusive rocks that are tilted about 10 to 15 degrees to the south. The low cuestas in the southern and central part of the range expose the upper part of the Hueco Formation of Wolfcampian age.

 

Kottlowski mapped the regional general geology and measured the stratigraphic column in his Las Cruces Quadrangle study (1960a). His measured section of the Hueco Formation is given as 1,715 ft. This thickness excludes the Wolfcampian Bursum Formation of 190 ft which should probably be included with the Hueco Formation in the Robledo Mountains (1,905 ft total adjusted Hueco Formation). Jordan (1971), who measured 175 ft of Bursum Formation, included this sequence in his Hueco Formation and arrived at a total thickness of 1,864 ft. W. R. Seager has completed the detailed general geology of the Robledo Mountains and has measured a section of the Hueco Formation that approximates Jordan and Kottlowski's figures (Seager, personal communication, 1974). All workers have informally divided the Hueco into lower, middle, and upper members with a tongue of the Abo Formation occurring between the middle and upper members.

 

An exceptional silicified phylloid algal bank was discovered in the upper member at the Shalem Colony section (sec. 19, T. 22 S., R 1 E.) in the summer of 1967 (LeMone and others, 1967). The study of this bank and the subjacent 275 ft of the Abo tongue was followed by a megafaunal and microfacies analysis (LeMone and others, 1971). This study has expanded into a rigorous examination of the megafaunal and lithologic relationships of the Abo tongue and upper Hueco member in the Robledo Mountains and other ranges in south-central New Mexico. A regional detailed examination of the entire Hueco Formation problem in Dona Ana County and areas to the south and west was initiated during the summer of 1974. This study will include the establishment of a transitional Abo-Hueco stratotype in the Robledo Mountains. This paper summarizes the progress on this problem to May, 1975 and is confined to a discussion of the Abo tongue and upper Hueco member in the Robledo Mountains.