Jurassic plutons of diorite to quartz diorite composition are present in a few ares within Elko County. A small dioritic pluton present in the Ninemile Mountain Quadrangle is considered Jurassic by Coats (1985). To the north in the Bull Run Quadrangle, the White Rock and Columbia stocks are hornblende diorite and hornblende-biotite quartz diorite respectively, and each cover an area of about 1 square mile (Decker, 1962). The White Rock pluton contains about 40 percent hornblende partially altered to chlorite and sphene (Decker, 1962). The Columbia pluton is dated at 149.7 +/- 5 Ma (Coats and McKee, 1972).