Perched on rocky crags near a roaring waterfall, two tiny human figures bear witness to the unspoiled beauty of their surroundings. Painted by William C.A. Frerichs immediately before the Civil War, Falls of Tamahaka is a highlight of "A Century of Nature: American Paintings 1855-1955" at Richard York Gallery on Manhattan's Upper East Side. Works in the exhibition range from the realism of the Hudson River School to the quick-brush Impressionists and the rule-breaking modernists.

Today's tight market for the work of the best-known American painters, particularly the Hudson River School artists and the early 20th-century modernists, has helped focus attention on lesser known artists like Frerichs and another Pennsylvania painter, William H. Willcox. Willcox's attractive 1867 Pennsylvania River Landscape ($60,000) depicts a sunny valley, with grazing cows and a lone boater on a meandering river.

Gallery owner Richard York explains his approach in this show by saying, "It's not the name that makes something good, but it's how it speaks to the time in which it was done, and how it stands in its own right." One pleasant surprise in the exhibition is a 1936 painting of tulips by Ida O'Keeffe ($65,000), conceived in a style similar to that of her older sister, Georgia O'Keeffe. Despite the intense rivalry between the sisters and Georgia's edict that Ida stop painting, York observed that in the end, "It's a good, solid modernist painting from the '30s."

In addition to capable but unfamiliar artists like Willcox and the younger O'Keeffe, "A Century" showcases a ca.1895 view of Shinnecock Hills by Impressionist William Merritt Chase ($650,000) and a light-suffused garden scene from 1926 by Theodore Earl Butler, who lived at Giverny and married into Monet's intimate family circle. A group of still-life paintings includes a highly detailed arrangement of fruit in a silver compote from the 1870s by Boston painter Taylor Buzzell and two paintings by Joseph Decker, one of which shows his tamed squirrel Bonnie surrounded by leaves and nuts.

Among the 20th-century material are simplified tree studies in tempura and starch from 1931 by Walter Beck and a semi-abstract watercolor of waves pounding the Maine shore by John Marin ($150,000). A Milton Avery from 1963, Gulls in Blue Sea ($225,000), combines three swathes of color to suggest yellow sand, a deep blue sea and light pink sky. Fountain ($800,000), painted by the stylistic wanderer Joseph Stella in 1929, is a surreal combination of an abstracted tree, curving human figure, swan and lotus.

Major museum exhibitions, like "American Sublime" at the Tate Britain in London, a show of Hudson River School painters, encourage viewers to reconsider the value of 19th- and early 20th-century American art. "A Century of Nature" is further proof that dealers and collectors are rethinking the standard history. "People have thought of American art as coming into its own post-WW II," explained York. "There were groundbreaking things that were being done prior to that, and I am glad to see that the attention is coming to it."