Diabase Sill and basement unconformity, view southward. The Crystal Spring Formation, which is the lower part of the Pahrump Group, rests depositionally on basement rocks. It is intruded by green-colored diabase sills that have yielded an age of 1.08 Ga (Heaman and Grotzinger, 1992). Metamorphic reactions between the diabase and dolomite of the Crystal Spring Formation produced large deposits of talc, which have been mined throughout the Death Valley region. To the south, this photograph shows the western edge of the southern Black Mountains, and in the distant background, the Avawatz Mountains.