1. Potentiometric surface, 1980, and water-level changes, 1969-80, in the unconfined valley-fill aquifers of the San Luis Basin, Colorado and New Mexico Yale Public content 1985. 2002-06-01T04:00:00Z. 2002-06-01T04:00:00Z. Geological Survey (U.S.). The Survey ; For sale by Branch of Distribution. English. Public. San Luis Valley (Colo. and N.M.).