FORT UKION OF CRAZY MOUNTA.IN FIELD, MONT. 13 



and its southern part mostly by Sweetgrass and Otter Creeks and 

 their tributaries, here running mainly southeastward. The extreme 

 northwestern part is drained by American Fork and Lebo Creeks, 

 tributaries of the Musselshell, and the extreme southwestern part by 

 Bigtimber Creek, tributary to the Yellowstone. Lebo and Fish 

 Creeks rise in this area and carry little water in ordinary weather, 

 while the other streams mentioned rise in the mountains and have 

 larger and more nearly permanent flow. 



Apart from the actual mountain area and its flanking zone of 

 pediments, moraines, and outwash, here poorly developed, this region 

 is a hilly one v/ith mature topography almost entirely determined by 

 the hardness and structure of the underlying rocks. The harder 

 sandstones form ridges and scarps, and the softer beds are eroded into 

 valleys or flats. The most striking elevations in the northeastern 

 part of the field, lilce Bear Butte and Lion Butte, are sandstone- 

 capped erosion forms. Cayuse Butte, a prominent but relatively low 

 and irregular mass, and Porcupine Butte, the most prominent eleva- 

 tion outside the mountains, also are supported by intrusive igneous 

 rocks (as are the mountains). The southern part of the field is hilly 

 but has no prominent topographic features. There are three small lakes 

 in the area, Lebo Lake in the northwest and Lakes Adam and Wal- 

 voord (more generally known as the Glass Lindsay Lakes) in the 

 southeast, all artificial and developed for irrigation. 



The highest point outside the mountains is Porcupme Butte, 6,970 

 feet, and the lowest is on Fish Creek where it leaves this area, about 

 4,000 feet. 



Climate and vegetation vary from mountain to high-plains types. 

 The mountain flanks have forest of lodgepole pine and other conifers, 

 with aspens along the streams and some colorful meadows, while the 

 main part of the field is very sparsely timbered, with evergreens on the 

 higher sandstone ridges and cottonwoods in wet valley bottoms. 

 The broad intervening areas, except for the relatively small uTigated 

 patches, are characterized by sagebrush, pricklypears, small yuccas, 

 and grass. Abandoned plowed land is taken over by weeds, especially 

 Russian thistles. In spite of the rather sparse nature of the vegeta- 

 tion, almost the entire area is sodded over. Shale exposures are small 

 and relatively few, and there are no badlands. 



The topography along the northern edge of the area (beyond the 

 Fort Union exposures) is very different, for here there are large, well- 

 developed, high, gravel-covered terraces cutting across the tilted 

 Cretaceous beds without regard for their hardness. s?.,| 



This general Fort Union area has received various designations, 

 such as "Fish Creek", "Bear Butte", "Sweetgrass County", or "Mel- 

 ville." Fish Creek is a minor stream draining less than half of the 

 region especially considered. Bear Butte is a small and marginal 



