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Any work that documents the path of a long-ago journey is bound to offer contrasts between old and new, and Greg MacGregor’s “Lewis and Clark Revisited: A Trail in Modern Day” is no exception. The exhibition of 40 black-and-white photographs begins, appropriately, where the famed expedition began in 1804: in St. Louis, where today a girder bridge stands, its bustling traffic mocking the explorers’ logistical challenges. Other images offer obvious counterpoints to days of yore—swooping elevated highways, deer killed by speeding vehicles rather than by hungry hunters, plastic buffalo-themed advertisements in place of real animals, a nuclear power plant, and a ladder that enables salmon to sidestep an enormous dam. But the old-new dichotomy is only a starting point for MacGregor. His most moving imagery documents more recent changes: a boulder sacred to the Mandan that was carelessly moved to a highway turnoff and later broke into three parts; a swimming pool in a “new town” constructed after seven American Indian villages were ruined by floodwaters; a lone, abandoned bridge piling standing sentinel in the Yellowstone River; and the unusual “eye of the needle” rock formation that partially collapsed in the 1990s, apparently due to natural weathering. The show ends on a hopeful note, with a photograph of an Osage orange tree in Philadelphia believed to have been grown from a cutting collected by Lewis. The milder climate of Philadelphia enabled the tree to reach twice its normal height, and it still produces fruit to this day. The show is on view from 8:30 a.m. to 4:30 p.m. Mondays through Fridays and from 1 p.m. to 4 p.m. the third Saturday of every month, through Tuesday, Feb. 28, 2006, at the Department of the Interior Museum, 1849 C St NW. Free. (202) 208-4743.