62 IOWA ACADEMY OF SCIENCES. 



Fork and Bear river is northward, in Utah, but on the 

 approach of Wyoming, flow northeasterly and then due 

 east and southeast into Green river, excepting Bear river, 

 which flows northward, around Bear lake, Anally empty- 

 ing its waters into Salt lake. The valleys have been 

 carved out of the horizontal strata. The lower ends of the 

 foothills are marked by high semi-arid table-lands, with an 

 entire absence of trees, except on the slopes. These table 

 lands are cut with canons in which a few shrubs like 

 A))iehuichier ahiifolia, and Siimphoricarpos racemosus are 

 types. 



The slopes usually contain a sparse growth of the west- 

 ern cedar {Juniperus occidentalis var monosperma). The 

 ends of these table lands are frequently more conspicu- 

 ously elevated and are called buttes. The Bridger Butte is 

 a good illustration of the type of formation occurring in 

 this section. Tenacious clay and broken fragments of the 

 Green river beds and the brown sandstone of the Bridger 

 group characterize the region. 



From the river bed of Black's Fork to the summit of the 

 table land a series of distinct flood plains occur, showing 

 a well marked progressive change in the character of the 

 vegetation. The limit of coniferous woods northward 

 along Black's Fork is 8,500 feet. The limit of the aspen 

 {Populus fremnloides), is somewhat lower, extending for 

 some distance beyond the Finns Murrai/ana belt. Beyond 

 these open table lands the country is cut with longer 

 canons, but it is possible to reach the source of the streams 

 bj an easy ascent to the high table lands at an elevation 

 of 10,000 to 11,000 feet. 



Near the old Ft. Bridger military reservation there are 

 three well-defined flood plains. The present flood plain is 

 an area abounding in trees of a mixed growth of conifers 

 and deciduous trees. It is essentially a mesophytic area, 

 with small hydrophytic basins, the current of the stream 

 being so rapid in most places that few of the higher hydro- 

 phytes can And lodgment. It is only through the seepage 

 of water in the smaller channels that these can And favora- 

 ble conditions for growth, or in the small streams coming 



