The
Guadalupe Mountains were first described in the reports of 1849 and 1850 United States military expeditions to the area. George Shumard was the first geologist to study the area, in 1855, and described an "upper white limestone" containing fossils. These included
fusulinids and
brachiopods, that were identified correctly by his brother, B.F. Shumard, as
Permian in age. However, debate on whether the beds were
Carboniferous or Permian in age continued until at least 1920. The work of Darton and Reeside in 1926 established the accepted framework for the stratigraphy of the area, and identified the Capitan Formation as
late Permian in age. Interest in the formation was rekindled by the discovery in May 1923 of the
Big Lake oil field in Texas and the drilling of the first commercial oil well in southeastern New Mexico in 1924. This culminated in the publication by E. Russell Lloyd in 1929 of his interpretation of the Capitan Limestone and associated formations as a gigantic fossil coral reef. Lloyd traced the reef nearly to
Carlsbad and noted that the dissimilarity of the formations on the two sides of the reef, now known as the basin and backreef shelf facies. Two months later, a “Symposium on Pennsylvanian and Permian stratigraphy of southwestern United States” appeared in the August, 1929 issue of the
Bulletin of the American Association of Petroleum Geologists, which provided a flood of new details on the Capitan reef. However, by 1937, King had concluded that the Tessey Limestone was not part of the Capital Formation and removed it as a member. By 1942 he had restricted the definition of the Capitan Formation to reef limestone, consistent with the stratigraphic conventions in the Guadalupe Mountains, and removed the Gilliam and most of the Vidrio Limestone from the formation. ==Description==