An older bioherm has contributed to the deposition of high-porosity reservoir rock and the creation of a trap in the San Andres Formation. Starting with almost 300 ft of relief, this mound was first "drowned" during a transgression and was later gradually buried by prograding, cyclic, subtidal to supratidal carbonates and anhydrites. 80 ft of relief presently exists on the base of the producing interval. Relief on the top is approximately 140 ft. Compaction drape accounts for only part of this relief. The mound was reflected as a shoal in the subtidal zone during the deposition of the producing interval. Relief in this shoal was maintained by higher depositional rates and by the deposition of relatively uncompactible, mud-free sediments in the crestal portion of the mound.--Modified journal abstract.