316 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
quaking aspen; next to a belt of spruce and fir; then out above 
the few stunted, highest growing individuals of these to the open 
alpine meadows and slopes. In this progress, corresponding to in- 
creased altitude, there is increased moisture. The alpine meadows 
are continually moist from more or less permanent snowdrifts, while 
here and lower on the slopes frequent showers occur in summer. 
The foothills exist as a particularly wide and definite zone to the 
east of the Southern Rockies, and a peculiar flora of foothill species 
extends from Las Animas County, Colorado, to Albany County, 
Wyoming. The Black Hills of South Dakota are essentially a 
foothill region. Ranges of foothills, with a characteristic flora, 
running through southwestern Wyoming, southeastern Idaho, and 
northern Utah, connect the Northern with the Wasatch Rockies. 
In Utah and western Colorado many of the ranges are equivalent 
to the mountain foothills. In their flora the low mountains, the 
foothills, and the lower slopes of the main mountain chains are 
identical. 
The different zonal treatments of the life of the Central Rocky 
Mountain States are based primarily upon the account and the 
classic map of Dr. C. Hart Merriam,' a map of the United States 
which, however, shows but little detail for this region. The work 
which Dr. Merriam then roughly outlined has, under his direction 
or stimulus, since been carried out in greater detail and made far 
more satisfactory by the United States Biological Survey. A series 
of state biological surveys has been begun, and for our area that 
for Colorado,’ by Merritt Cary, was published in 1911, and that for 
Wyoming,’ by the same author, in 1917. These contain excellent 
maps and interesting and pertinent text. His discussion is based 
upon personal field study, including practically every portion of 
these states and botanical even more than zoological evidence. 
The maps, slightly modified, as explained below, have been my best 
guide in expressing the zonal distribution of species. 
In the plant distribution of the area covered by my study, Dr. 
Rydberg has been especially interested. In the Bulletin of the 
Torrey Botanical Club he is publishing a series of sketches of Rocky 
Mountain vegetation, zone by zone; but the paper which logically 
introduces these sketches and gives the author’s delimitation of 
each zone is one published in the Memoirs of the New York Botanical 
Garden.* I am greatly indebted to this outline and to an unpublished 
1 Life zones and crop zones of the United States, by C. Hart Merriam. U.S. Dept. 
Agr. Biol. Surv. Bull. 10. 1898. 
2 A biological survey of Colorado, by Merritt Cary. U.S. Dept. Agr. N. Amer. 
Fauna 83. 1911. 
3 Life zone investigations in Wyoming, by Merritt Cary. U.S. Dept. Agr. N. 
Amer. Fauna 42. 1917. 
* 6: 477-499. 1916. 
