In North America, hemlocks are also attacked by hemlock looper. The hemlock woolly adelgid has destroyed most of the hemlocks within the park. Along the Pacific coast, redwood, Sitka spruce and hemlocks predominate as overstory cover. The eastern hemlocks around Spruce Creek below Kaaterskill Falls are also a virgin stand. There are groves of mature Eastern hemlocks that may have been mistaken for pine trees. Often cool, moist shaded ravines are dominated by pure stands of hemlocks in this range. Diameters of mature hemlocks range from , with trees over in diameter being very rare. The southern part of this glen has large areas of old-growth forest, chiefly hemlocks. Much of the railroad was built of trestles constructed from the region's native hemlocks. However, not all the old hemlocks were harvested. Western hemlocks can reach over in height with a diameter of . The hemlocks (or similar-looking plants) in the wood were said to have inspired his verse. Around the mark the trail crosses Pennsylvania Route 44 in a stand of hemlocks. Two Western Hemlocks, the state tree since 1947, flank the seal's outer edges. Hemlocks in particular are most likely to host Blackburnian warblers in mixed forests.