Geology of the Grayback Mining District, Costilla County, Colorado, 1910, by H.B. Patton, C.E. Smith, G.M. Butler, and A.J. Hoskin. 111 pages. 9 plates. Digital PDF download. B-02D
Excerpted from the report:
The area surveyed embraces about thirty square miles in the northern part of Costilla County, Colorado, lying due east of Blanca Peak, the highest peak of the Sangre de Cristo Range. The Sangre de Cristo Range, which starts opposite Salida, runs approximately south until it culminates in Blanca Peak, which rises to a height of considerably over 14,000 feet. At Blanca Peak the range suddenly turns to the northeast, and runs for some fifteen miles at a much lower level, turning again to the southward at Sangre de Cristo pass, and finally merging into the Culebra Range. The county line between Costilla and Huerfano counties follows this lower portion of the Sangre de Cristo Range, and likewise forms the northern boundary of the mapped area. The southern, western and eastern boundaries have been taken somewhat arbitrarily, but so as to include the town of Russell, formerly called Placer.
Field work was accomplished during the summer of 1909 and photographs of the area taken during the field work are included along with a claims map.
The report is organized into the following chapters: Chapter I. Introduction; Chapter II. Topography; Chapter III. Archean geology; Chapter IV. Sedimentary rocks – Carboniferous; Chapter V. Igneous rocks; Chapter VI. Contact–metamorphic rocks and iron ores; Chapter VII. Ore deposits; Chapter VIII. Mines and mining processes; and Chapter IX. Orographic movements and bibliography.