STS090-751-018 Nacimiento Fault, New Mexico, USA April 1998 Most of the time in nature straight lines do not occur but in this scene the north-south aligned Nacimiento Fault presents a dramatic boundary, seen here extending from near the top left corner towards the center of the view. The boundary clearly demarcates the elevated Precambrian rocks of the San Pedro Parks, which appear wooded and therefore darker (lower left) from the sedimentary rocks of the lower San Juan Basin, where drier grasslands appear light brown (mainly in the upper half of the view). Several dry stream channels which only flow intermittently can be discerned in this part of the San Juan Basin, which lies generally less than 7000 feet (2134 meters) above sea level. Streams on the eastern side of the fault follow a series of deeply incised river valleys as they flow south around the west side of the Valles Caldera. Some of the individual cinder cones within the Valles Caldera are visible in the east corner (bottom left) of the image. The snow-covered plateau (just below the center of the picture) has elevations of more than 10,000 feet (3234 meters) above sea level so that cold temperatures preserve the snow cover.