WASHINGTON — In 1842, America was still young, incomplete and sadly lacking in monuments that might declare it singular. A photograph of Niagara Falls was the only American image included that year in a French picture book of “the most remarkable monuments of the globe.” Western explorations would record landscape prodigies later, but Americans had long been awe-struck and inspired by the lesser but still mighty Northeastern wilderness. The Hudson River School of painters, founded in 1825 by Thomas Cole, portrayed that landscape as a path to the sublime, and citizens hastened out of crowded cities to follow that path. When photography was widely introduced in 1839, photographers came too, lured by the glories of the Catskills in New York and the White Mountains of New Hampshire.

Eastern landscape photographs have been largely eclipsed by images of spectacular Western sites. (Perhaps the popularity of Ansel Adams’s pictures helped establish a taste for the similar spirit of the early Western photographs.) “East of the Mississippi: Nineteenth-Century American Landscape Photography” at the National Gallery of Art here is the first comprehensive museum show to turn a light on this era of Eastern landscape photographs. Diane Waggoner, curator of 19th-century photographs, has assembled 175 images from the medium’s infancy, in 1840 to 1898; she is also chief author of the exhaustively researched catalog.

Eastern landscape images, sometimes beautiful, sometimes grand, spurred tourism and development. Seneca Ray Stoddard’s “Avalanche Lake” (circa 1880) promised wilderness lovers that beetling cliffs, halcyon lakes and nature’s whispers to the longing soul were still rife in the Adirondacks. A few paintings of similar scenes and themes, testaments in gilded frames to different media walking hand in hand across rough ground, are deftly inserted between black-and-white forests, waterways and mountains. Yet often the land played second fiddle to the breakneck pace of transformation in the century.

Lesser known names like Isaac H. Bonsall, Henry Peter Bosse, Thomas M. Easterly, Josiah Johnson Hawes and others have pride of place. Bonsall’s photograph of a landscape near a battlefield, taken during the Civil War, is an artful surprise. Perfectly peaceful, it centers on a waterfall plunging down a sweeping curve of rock, with soldiers posing before it. As cameras were too slow back then to stop action, landscapes became war reports: Here are encampments, here is a battlefield (the bodies lie below), here a general died. Most wartime photographs were not quite so explicitly artistic as Easterly’s; late in the century, photographers insisted more ardently that they were artists. Yet wartime landscapes doubtless created memories, even imaginary memories of war.