The most common deciduous tree in the park is QUAKING ASPEN. It is immediately recognized by its smooth, white bark and small, green leaves that tremble with the slightest breeze, because of the curious flattening of the petiole, or leaf stalk, at right angles to the leaf blade. Aspen grows to considerable size in beautiful groves of tall trees, where the moisture and shelter are sufficient, but is more often seen in scrubby thickets on rocky, drier slopes. In September the leaves turn to a golden color, giving early autumn travelers a matchless visual experience. NARROW-LEAF COTTONWOOD grows along streams in the lower altitudes of the park. Many willows also occupy streambank environments, the most common being SCOULER WILLOW with characteristic willow leaves and large oval catkins, which are quite conspicuous in May and early June. WATER BIRCH is a thin-leaved, graceful shrub, sometimes growing to tree size, commonly seen along streams in the lower forests. It can be recognized by its graceful, almost delicate appearance. THINLEAF ALDER, also abundant along streams, often grows in great clumps with many stems growing from the same root. Widespread throughout the West, the alder provides habitat for many bird groups. You may also recognize, by its leaf, ROCKY MOUNTAIN MAPLE, which grows here and there in the park up to about 11,000 feet. The shrubs most commonly observed by the visitor are: ANTELOPE BITTERBRUSH—a low, tough, much-branched shrub, with many fragrant, pale-yellow blossoms in May and June. Its leaves are less than 1 inch long, wedge-shaped and 3-toothed at the apex. The spindle-shaped seeds are important food for chipmunks and ground squirrels, and mule deer depend on the shrub for browse. BOULDER RASPBERRY—a common bush with showy, 5-petaled white blossoms, up to 3 inches across. During May and June this shrub adds much beauty to the landscape. Birds eat its berries avidly. WAX CURRANT—a common shrub found also in the highest forests—forms rounded clumps, 1 to 3 feet high, with rigid, much-branched stems and rounded leaves. The red berries ripen in summer and are eaten by many birds and small rodents. This plant is alternate host to blister rust (a disease which may affect the limber pine in the park in the near future), and much of it has been eradicated in areas where limber pine grows. SAGEBRUSH—a familiar plant in much of the West—in this park grows in a dwarf form, and is common in Glacier Basin and on the southwest slopes of Deer Mountain. This woody shrub, about 1 foot high, with 3-toothed, wedge-shaped, silvery leaves, is good forage for mule deer. Conspicuous wildflowers that grow below 9,000 feet in the park and that will attract attention in their blossoming season are: