The Shasta–Trinity Forest lies at the intersection of the Eastern Klamath Mountains and the Southern Cascades (Miles & Goudy, 1997). The land is largely forested, though at low elevations there are areas of
chaparral,
woodland, and
grassland. At high elevations in the Trinity Alps, Eddys, and Mt. Shasta, forest gives way once again to montane chaparral, subalpine woodlands, and ultimately to alpine rock and scree. Starting with lower elevations in the foothills around Shasta Lake, north of Redding, the forests and woodlands are dominated by
gray pine,
knobcone pine,
ponderosa pine,
blue oak,
black oak,
canyon live oak,
Douglas fir, and
white oak. Shrub diversity is very high. Common understory shrubs at lower elevations are
whiteleaf manzanita,
wedgeleaf ceanothus,
California buckeye,
California coffeeberry and
western redbud. In moist stream canyons, other trees and shrubs prevail—
bigleaf maple, western spicebush (
Calycanthus Occidentalis),
dogwood,
white alder, and
willows. At mid-elevations
sugar pine,
incense-cedar,
white fir and
Jeffrey pine join Douglas-fir, ponderosa pine, and canyon live oak, while the other pines and oaks drop out of the mix.
Huckleberry oak, shrub
tanoak,
greenleaf and
pinemat manzanitas, and
bush chinquapin, are important understory components. In the Cascades east and north of Mt. Shasta,
bitterbrush and
tobacco brush are very common. On the serpentines of Trinity County's mid-elevation Klamath Mountains, incense-cedar and Jeffrey pine woodlands are inhabited by shrubby Congdon's silktassel, leather oak, and hoary manzanita. Farther west, on the long ridge of South Fork Mountain that divides the Shasta–Trinity and Six Rivers National Forests, the tree form of tanoak grows mixed with Douglas-fir and golden chinquapin. Upper montane and subalpine forests in the Klamath Ranges are characterized by a mix of tree species including red fir, mountain hemlock, foxtail pine, and lodgepole pine. At higher elevations, Western white pine and whitebark pines dominate the landscape. Montane meadows and streamsides in this region boast a diverse flora featuring abundant California pitcherplant and western azalea. Occasionally, the Port-Orford-cedar can also be found here, distinct from its usual coastal habitats. Much more detail on the vegetation zones of Mount Shasta, and their associated flora and fauna, can be found in C. Hart Merriam's important early biological survey, published in 1899. ==Lakes and rivers==