. A biological survey of Colorado. Natural history Colorado; Mammals Colorado; Trees Colorado. TREKS AND SIIIUJBS. 227 I'oi- sojuo (listjincc. It is usually associutcd with narrow-leaved cottoiiwoods and willows, and I have seen it only near stream banks. In July, 1007, I found several large clumps fully 20 feet in height on Dolores River near the mouth of West Creek, at 5,000 feet. The s])e('ies occurs regularly up to 8,000 and occasionally to 9,000 feet tluough the entire width of the Transition zone. I did not observe it in the Canadian zone. I found B. fontinalis common at the following lo
. A biological survey of Colorado. Natural history Colorado; Mammals Colorado; Trees Colorado. TREKS AND SIIIUJBS. 227 I'oi- sojuo (listjincc. It is usually associutcd with narrow-leaved cottoiiwoods and willows, and I have seen it only near stream banks. In July, 1007, I found several large clumps fully 20 feet in height on Dolores River near the mouth of West Creek, at 5,000 feet. The s])e('ies occurs regularly up to 8,000 and occasionally to 9,000 feet tluough the entire width of the Transition zone. I did not observe it in the Canadian zone. I found B. fontinalis common at the following localities: vStreams of Koutt County; North Park; Plateau Creek; Bailey; Lake George; wSt. Elmo; Frying Pan River, Basalt to Peachblow; head of Smith Fork, West Elk ^Mountains; Una weep Canyon; Placerville; Durango; Rico; Mancos; Ba}'- held; and La Yeta. Betula glandulosa. Dwarf Birch, The habitat of the dwarf birch is along the borders of cold bogs and streams in the higher moun- tains, between 9,000 an-d 11,000 feet, in the upper Canadian jind lower Iludson- ian zones. It has been foimd on prac- tically all the higher mountain ranges of the State. The nor- mal growth is from 3 to 5 feet high, but in the Hudsonian zone at about 11,000 feet the species is dwarfed, rarely exceeding 2 feet. It was particularly abundant in 1906 in the mountain meadows on the Park Range and on the mountains east of Laramie River, where a low, dense growth fringed most of the bogs between 9,000 and 10,000 feet. I saw it on Grand River, 5 miles east of Hot Sulphur; on the San Juan Mountains near Ophir, at 10,500 feet; and southeast of Lake City, 9,000 to 11,000 feet. The leaves were falling near Lake City, October 18, 1907. Alnus tenuifolia. Alder. Alders form a dense fringe along cold streams throughout the Colorado mountains. They are most abundant in the Canadian. Fig. 35.—Alpine ^vlllows in Arctic-Alpine zone, Front Range, near Ber- thoud Please note that these images are extracted from sc
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