Context of Background information to accompany folio of geologic, mineral resource, geochemical, aeromagnetic, and gravity maps of the Hillsboro and San Lorenzo quadrangles, Sierra and Grant Counties, New Mexico, by D. C. Hedlund ; with sections on geochemistry by K. C. Watts and H. V. Alminas, and geophysics, by J. C. Wynn and D. C. Hedlund, (electronic resource)