Apollo 17 metric photographs (fig. 29-26) provide the best available coverage for geologic interpretation of northern Mare Crisium and the northern Crisium basin. The area was covered previously by low-resolution telescopic and Lunar Orbiter IV photographs and by oblique, high-illumination, or low-resolution photographs from earlier Apollo missions. One region in particular, between Alhazen Crater and longitude 66° E, had previously been covered very poorly. The Apollo 17 photographs provide excellent monoscopic (fig. 29-26) as well as stereoscopic viewing because of the favorably low Sun illuminations (15° to 49°). These new photographic data allow the geology of the basin, the mare, and other nearby terrains to be reevaluated. This reexamination together with data from continuing Moon-wide photogeologic studies and analyses of returned rocks from Apollo landing sites, has produced a simple evolutionary picture of the region, expressed by fewer map units and explained by fewer basic processes than previously thought necessary (refs. 29-35 and 29-45 to 29-48).
