Named for Routt Co, CO. Occurs in the Rawah batholith in the Park and northern Gore Ranges, CO and Medicine Bow Mountains, WY. The Rawah (type area) and other plutons (reference localities) are in the Southern Rocky Mountain region. The rocks are catazonal and synorogenic in habit, concordant, commonly foliated, and are mainly granodiorite to quartz monzonite. Divided into unnamed granitic and gabbro bodies, and into nine formally named units (Boulder Creek and Cross Creek Granites or Granodiorites, Twin Spruce Quartz Monzonite, Denny Creek, Kroenke, and Pitts Meadow Granodiorites, Powderhorn, Bakers Bridge, and Tenmile Granites). Belongs to the 1,700, or Early Proterozoic age group. Rawah is 1,665-1,675 m.y. (Rb-Sr).

Source: GNU records (USGS DDS-6; Denver GNULEX).

Mount Evans batholith is exposed over a 225 sq km area in the Front Range of CO in the Southern Rocky Mountain region. The batholith is composed of weakly to strongly foliated, medium- to coarse-grained gray monzogranite and granodiorite, and includes several small plutons called granite of Rosalie Peak. The Mount Evans characterized by foliation caused by igneous flow structure. It was previously considered to be a part--one of the unnamed granitic bodies--of the Routt Plutonic Suite of 1.7 Ga. New U-Pb zircon ages on four samples from the batholith and from the granite of Rosalie Peak indicate an emplacement age of 1442 +/-2 Ma. It is chemically different from most of the other 1.4 Ga granites. Different chemistry due to different source areas, or it may have been derived from different depths. Mount Evans and the granite of Rosalie Peak are reassigned to the 1.4 Ga Berthoud Plutonic Suite as one of the unnamed granitic bodies.

Source: GNU records (USGS DDS-6; Denver GNULEX).