=_Eutamias minimus consobrinus_= (J. A. Allen).--The 63 specimens of the Least Chipmunk (59770-59824, 60105-60108, 70024-70025, and nos. 5194 and 5196 in Univ. of Colorado Museum) were taken at localities 2, 3, 4, 6, 7, 8, 10, 13, and 15. The reproductive condition at time of death had been noted for 20 females obtained from June 17 to July 2 at elevations from 9500 to 10,400 feet. Eleven of these had no embryos, but six have mammae that are still prominent on the dried skins and may have had litters prior to their capture. Nine females contained embryos, numbering 3 in two specimens, 5 in four specimens, 6 in two specimens, and 7 in one specimen. =_Eutamias quadrivittatus hopiensis_= Merriam.--Four specimens of the Colorado Chipmunk were obtained by D. A. Sutton at locality 2, at 6800, 6900, 7175, and 8050 feet elevation. All are males taken on May 13 and 14, 1949; the specimens bear numbers 5197, 5198, 5199, and 5201 in the collection of the University of Colorado Museum. =_Thomomys talpoides fossor_= J. A. Allen.--The 27 specimens of the Northern Pocket Gopher (59840-59849, 70086-70102) were trapped at localities 3, 6, 7, 10, 11, and 13. The eight skins from locality 7 differ from those from the other localities on the Mesa in being uniformly duller in color dorsally. No significant difference in size or cranial characters was observed. Specimens assigned to _T. t. fossor_, in the collection of the Museum of Natural History, from other localities in Colorado differ in color from any of the specimens from the Grand Mesa. Until larger numbers of _Thomomys talpoides_ from other localities in Colorado and from the type locality of _T. t. fossor_, stated to be at Florida, in southern Colorado, have been studied, the specimens from the Grand Mesa seem best referred to _T. t. fossor_. Three females from localities 7, 10, and 11 contained embryos (2, 4, and 5 in number), and seven other females from localities 6 and 7 show distinct mammae on the dried skins or were recorded by the collectors as lactating. =_Castor canadensis concisor_= Warren and Hall.--Dams constructed by beavers were seen at locality 4 on June 23, 1954. No specimen was taken. =_Peromyscus maniculatus rufinus_= (Merriam).--The 36 specimens of the Deer Mouse (59921-59956) are from seven localities (3, 4, 6, 10, 12, 14, and 15). The mice vary considerably in color; most of them are like mice of the highlands of Colorado and unlike the paler mice inhabiting the lower areas immediately to the west of the Grand Mesa. Young individuals trapped on June 20, 21, and 22 and judged to range from a month through two months in age, and females containing embryos, attest to a somewhat protracted breeding season on the Grand Mesa. =_Neotoma cinerea arizonae_= Merriam.--Two immature Bushy-tailed Wood Rats (60000-60001) were obtained at locality 3 on July 3.