2 UNIVERSITY OF MISSOURI STUDIES [150 



the Atlantic. Since this barrier is almost everywhere above 

 timberline, only a few Pacific species are found on the Atlantic 

 side of the slope within the region about Boulder. Perhaps 

 the most interesting exception is the occurrence of one of the 

 orchids, Piperia Unalaschensis (Spreng.) Rydb., a few indi- 

 viduals of which I found in the foot-hills near Boulder, and 

 which is not known to occur elsewhere east of the mountains 

 of Utah, it having its main range from Alaska to California. 



All the streams of Boulder County flow ultimately into the 

 South Fork of the Platte river, and thence into the Missouri 

 and the Mississippi. Boulder creek, the chief stream of the 

 region, and one of the headwaters of the Platte, is fed from the 

 snows of the Divide, especially between Arapahoe and James' 

 Peaks. Just over the other side of the Divide are some of the 

 headwaters of Grand river, which flows into the Colorado, 

 and thence into the Gulf of California. 



All the main streams in Boulder County have their sources 

 in the wasting snows of the Main Range. These have cut gor- 

 ges, in most cases over a thousand feet deep, into the elevated 

 plateau between the main range and the foot-hills proper, and 

 by means of these deep valleys have transformed this plateau 

 into what are now really mountain masses, having an average 

 altitude of about 8,000 feet, the eastern and western slopes of 

 which are long longitudinal valleys, and the northern and 

 southern ones the precipitous gorges cut by the streams. Be- 

 tween Boulder and the Main Range there are about four of 

 these mountain ridges, the first, or that of the foot-hills proper, 

 rising to a height of from 7,000 to 8,600 feet, the others slightly 

 lower, having an altitude of about 7,500 to 8,000 feet. Among 

 these Sugarloaf Mountain stands out prominently as an 

 isolated peak a thousand feet higher, it being a por- 



