Uranium deposits in the Espanola Basin, Santa Fe County, New Mexico
— Virginia T. McLemore, David Vaniman, Dennis McQuillan, and Patrick Longmire

Uranium mineralization in the Española Basin is not of sufficient quantity and quality to justify mining at the present time. However, many private water wells in the region produce water with concentrations of uranium (up to 1,820 pg/L (ppb)) that exceed the safe drinking water standard of 30 µg/L. Therefore, it is important to understand the source of the uranium in the groundwater and the processes involved. Potential sources for uranium in the groundwater include 1) uranium occurrences in the Tesuque Formation (San Jose mining district), 2) rhyolitic volcanic ash beds and sandstones with volcanic detritus found interbedded within the Tesuque Formation, 3) veins, replacements, and pegmatites in Proterozoic rocks (San Jose and Nambe mining districts), and 4) Proterozoic granitic rocks in the Sangre de Cristo Mountains.

The sandstone uranium occurrences in the Tesuque Formation represent natural precipitation and concentration from ura­niferous groundwaters, likely derived from 1) rhyolitic volcanic ash beds within the Tesuque Formation, 2) the alteration of granitic and/or volcanic detritus within the sedimentary host rocks, and 3) Proterozoic rocks in the Sangre de Cristo Mountains to the east. One property, the San Jose No. 13 (NMSF0033), produced 12 lbs (5 kg) of U₃O₈ at a grade of 0.05% U₃O₈ in 1957. Uranium in modern groundwaters likely was derived from the same sources, as well as from leaching and oxidation of older uranium occurrences in the Tesuque Formation. Uranium then precipitated from the waters to form the geochemical anomalies found in the prospects.