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Colorado's Ecosystems: Pinyon-Juniper Woodland
Pinyon-Juniper woodland, affectionately nicknamed "PJ", dominates the slopes above the sagebrush and below the ponderosa pines in southern and western Colorado. This dry forest is highly distinctive both in appearance and in biodiversity. Neither the pinyon nor the juniper usually grows higher than about 10 feet tall, and both tend to grow widely spaced. Bird species that breed almost exclusively in or near pinyon-juniper in Colorado include Black-chinned Hummingbird, Cassin's Kingbird, Gray Flycatcher, Gray Vireo, Pinyon Jay, Bewick's Wren, Juniper Titmouse, Bushtit, Black-throated Gray Warbler, Black-throated Sparrow, and the rare but spectacular Scott's Oriole. In addition, this habitat may host Common Poorwill, Ash-throated Flycatcher, Plumbeous Vireo, Blue-gray Gnatcatcher, and Western Scrub-Jay. In winter it can be crawling with mixed-species flocks of thrushes, including American Robin, bluebirds, and Townsend’s Solitaire. Summer brings distinctive butterflies such as Desert Marble, Juniper Hairstreak, Indra Swallowtail, and Great Basin Woodnymph.
The highest diversity in this habitat is probably along the Utah line, where species like Cliff Chipmunk barely enter the state. The high-quality pinyon-juniper habitats closest to Denver are in the Radium area (Grand and Eagle counties), the Buena Vista area (Chaffee County), and the Canon City area (Fremont County).
Rimrock is the term for the distinctive outcrops that can run for miles in the same geological layer, forming the rims of valleys and mesas in the southwest part of the state, parts of the Arkansas River Valley, and other scattered locations. Characteristic of some of the state’s most scenic areas, including Colorado and Dinosaur National Monuments and Mesa Verde National Park, rimrock tends to be associated with pinyon-juniper habitats. Birds associated to a strong degree with rimrock in Colorado include Chukar, Greater Roadrunner, Canyon Wren, Canyon Towhee, and Rufous-crowned Sparrow. Raptors often nest on the cliff faces, and rimrock can also be a good place to look for wildlife including bighorn sheep, mountain lion, the spectacular collared lizard, and the rarely-seen ring-tailed cat.