524 



NATURALIST'S GUIDE TO THE AMERICAS 



Bruner, L., Wolcott, R. H., and Swenk, 

 M. H. A Preliminary Review of the 

 Birds of Nebraska. Ann. Rept. Neb. 

 State Bd. Agric. for 1903. Also 

 separate. 125 pp. 1904. 



Condra, G. F. Geography of Nebraska. 

 192 pp. Lincoln, 1906. 



Petersen, N. F. The Flora of Nebraska. 

 220 pp. Lincoln, 1912. 



Pool, R. J. A Study of the Vegetation 

 of the Sandhills of Nebraska. Minn. 

 Bot. Studies, IV, 189-312, pis. XXVI- 

 XL, and map. 1914. 



Pool, R. J., Weaver, J. K, and Jean, 

 F. C. Further Studies in the Ecotone 

 between Prairie and Woodland. Uni. 

 Neb. Studies, XVIII, 1-47, figs. 1918. 



Pound, R., and Clements, F. C. The 

 Phytogeography of Nebraska. 443 

 pp., 4 maps. Lincoln, Nebr., 1st ed., 

 1897; 2ded., 1900. 



Swenk, M. H. A Preliminary Review 

 of the Mammals of Nebraska. Stud. 

 Zool. Lab. Uni. Neb., No. 89. 88 pp. 

 Lincoln, 1908. 



Thornber, J. J. Studies in the Vegeta- 

 tion of the State. I. The Prairie- 

 grass Formation in Region I. Rept. 

 Bot. Surv. Nebr., V, 29-143. 1901. 



Weaver, J. E., and Thiel, A. F. Ecologi- 

 cal Studies in the Tension Zone 

 between Prairie and Woodland. Bot. 

 Surv. Neb.; N. S., No. 1, 1-59, figs. 

 1917. 



Wolcott, R. H. Biological Conditions 

 in Nebraska. Publ. Neb. Acad. Sci., 

 VIII, 23-34, map. 1906. 



Woleott, R. H. An Analysis of 

 Nebraska's Bird Fauna. Proc. Neb. 

 Orn. Union, IV, 25-55, 6 pis. 1909. 



4. COLORADO 



BY FRANCIS RAMALEY AND W. W. 

 ROBBINS 



I. GENERAL 



Colorado is a state with many differ- 

 ent environments. One may travel 

 from the Great Plains of the eastern 

 part of the state or from the warm 

 valleys of the Western Slope to the 

 crest of the Continental divide and pass 

 through as many distinct climates as in 

 journeying from Virginia to arctic 

 Greenland. The lowest point in Colo- 

 rado has an elevation of 3386 ft. and the 

 highest 14,402 ft.; the altitudinal range 

 is therefore 11,016 ft., and it is this great 

 variation in altitude which determines 

 the differences in climate. 



Topographically the state consists 

 of three main parts: the Great Plains, 

 the mountains, and the western plateau. 

 The principal rivers are the South 

 Platte, Arkansas, Rio Grande, Colorado, 

 Grand, and White. All streams in the 

 densely populated areas are more or 

 less polluted and in periods of active 

 mining may contain objectionable mill 

 tailings which, however, seldom destroy 

 aquatic life. 



The Great Plains, comprising the 

 eastern two-fifths of the state, are 

 covered chiefly with short grass. This 

 association is almost uninterrupted 

 except for fringes of cottonwoods and 

 willows along water courses. In a few 

 favored places there is a prairie-grass 

 vegetation. On the divide between the 

 Platte and Republican rivers there are 

 some areas of sand hills with their 

 peculiar plant growth. The two chief 

 grasses of the plains are buffalo grass 

 (Buchloe dactyloides) and grama grass 

 (Bouteloua gracilis). In the early days 

 there were large herds of bison (Bison 

 bison} and prong-horn antelope (Anti- 

 locapra americana). The bison is no 

 longer found in the wild state and 

 antelopes are few in number. Of 

 small mammals, mention may be made 

 of the black-tailed prairie-dog (Cynomys 

 ludovicianus), yellow pocket gopher 

 (Geomys lutescens), Richardson kan- 

 garoo rat (Dipodomys ordii richardsoni} , 

 white-tailed jackrabbit (Lepus town- 

 sendii campanius), plains cottontail 

 (Sylvilagus audobonii baileyi), and plains 

 coyote (Cam's nebracensis) . 



The high mountains of Colorado trend 

 north and south, occupying the entire 

 central portion of the state. The 

 eastern slope of the mountains has a 

 chaparral belt between the grassland 

 and the forests of rock pine (Pinus 

 scopulorum) on the foothills. To the 

 north, this narrow interrupted belt of 

 shrubs and small trees is mainly choke- 

 cherry and thornapple in the moister 

 places with three-leaved sumac (Rhus 

 trilobata) and mountain mahogany (Cer- 

 cocarpus parvifolius) in drier situations. 

 In southern Colorado the chaparral 



