2 CONTRIBUTIONS TO PAL^ONTOLOGY 



generously loaned by the New York Botanical Garden. Competent field assistance 

 was rendered by Beverly Wilder of Antioch College, H. H. Sharkey of Princeton 

 University, and Ruth K. Dorf. 



FlG 



1 — Index map, showing location of Localities P. 371 to P. 376. 



PRESENT PHYSICAL CONDITIONS AND VEGETATION 



Of the 6 locaUties studied, 4 are situated in southern Wyoming and the remain- 

 ing 2 in northwestern Colorado, as shown in figiu-e 1. Both areas are essentially 

 alike in physical and climatic conditions and differ only in details with respect to 

 the type and distribution of vegetation. 



These areas are included in the high, barren intermontane basins of the Rocky 

 Mountain system. Their average elevation ranges from approximately 5000 to 

 7000 feet. The topogi-aphy is sub-maturely dissected, and largely controUed by the 

 differential erosion of variously dipping strata of unequal hardness. The southern 

 Wyoming region Ues in the drainage area of the North Platte and Medicine Bow 

 rivers, which are the only permanent streams. The Yampa River drains the area in 

 northwestern Colorado. Thc narrow flood plains of these streams are features of 

 primary importance in the distribution of modern vegetation. 



On the basis of moisture and temperature conditions these areas are near the 

 eastern edge of the cool, arid cUmatic province.^ Normal annual precipitation 



> Livingston and Shreve, Carnegie Inst. Wash. Pub. No. 284, 380, 1921. 



