States analyzed: Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, North Dakota, Oregon, South Dakota, Utah, Washington and Wyoming

Total area analyzed: 860 million acres, about half the land area of the lower 48 states

Area currently off-limits to development: About 128 million acres, or about 15 percent

Most common areas protected from development: Roadless areas and designated wilderness areas managed by the U.S. Forest Service, units of the national park system managed by the National Park Service, and wilderness areas and wilderness study areas managed by the U.S. Bureau of Land Management (see Glossary for an explanation of terms)

States with highest percentage of protected area: Idaho, about 29 percent; California, about 25 percent; Utah, about 21 percent; Nevada, about 16 percent; Washington, about 15 percent. For all other western states, our data indicate that less than 15 percent of the total land area is protected from development for renewable energy projects.

Other observations: More than two-thirds of the protected areas occur in just six of the 13 states: Arizona, California, Idaho, Montana, Nevada and Utah