Abstract Most of Mount Mazama lies within Crater Lake National Park in southern Oregon; its lower flanks are within Rogue River and Winema National Forests. Access to the rim of Crater Lake caldera is excellent, via paved roads from Oregon 62 and 230, but Mazama’s flanks within the park are generally only reachable by hiking trails. This guide serves for a long one-day excursion through the park, concentrating on features near the caldera rim road, with additional points of interest that could be visited on a second day. New U.S. Geological Survey 7 1/2-minute topographic maps covering Mount Mazama and adjacent areas were published in 1985 at a scale of 1:24,000. The existing 1:62,50 scale topographic map (Crater Lake National Park and Vicinity, 1956) was not made by modem methods, and the information on roads is not current. This map is in revision, and a modem version is expected shortly. Up-to-date information on access, accommodations, and visitor services can be obtained from Crater Lake National Park. The brochure entitled “Crater Lake,” which contains an adequate road map of the park at approximately 1:85,000 scale, is available at the park entrance booth, visitor center (Rim Village), or park headquarters. July and August are the best months to visit the park. In most years, snow limits access to the caldera rim through June, and early fall storms may interfere with a trip in September. It is wise to contact the park for information on early summer or fall snow conditions and to be prepared for thunderstorms or cold weather at any time.