The Skelly Oil Company's Hankins well No. 1 in southeastern Baca County, Colorado, low on the southeast flank of the Las Animas arch, penetrated a sequence of Paleozoic rocks about 5,500 feet thick, before being abandoned at a depth of 6,171 feet in the Arbuckle limestone. The sequence is, in general, similar to that present in southwestern Kansas, and includes formations of Permian, Pennsylvanian, Mississippian, Ordovician and Cambrian age. Nearly three-fourths of the sequence is absent in the Marland Production Company's Mesa well No. 1 and the Phillips Petroleum Company's Haskins well No. 1 near the crest of the arch. There, beds of Permian age overlie a thin remnant of the Arbuckle limestone which, in turn, overlies rocks of pre-Cambrian age. Pennsylvanian rocks of co siderable thickness are present on the west flank of the arch, as revealed by the Carter Oil Company's stratigraphic test No. 1 in southwestern Otero County. The Mississippian formations, and the Viola limestone and Simpson group of the Ordovician system are absent in the Carter well, however, and beds of Morrowan age overlie the Arbuckle limestone which, in turn, overlies rocks of pre-Cambrian age.