A warm (21-24°C) spring issues from alluvium adjacent to limestone at Thompson Ranch on the east side of Diamond Valley in Sec. 3, T23N, R54E (Mifflin, 1968). This spring may be the same as the Jacobson Ranch Springs reported by Waring (1965). Harrill (1968) suggested that the spring is probably fault-controlled, because it is part of the range front along the edge of the Diamond Range, according to Roberts and others (1967).