From 1870 to 1920, while successive schools of Paris were revolutionizing the Western art world, an even more astonishing revolution was taking place in a quite different Western art world.

This was the realm of the Pomo Indians of Northern California, whose life was forever altered by the Gold Rush of 1849 and California statehood the following year. With the flood of whites into the area, the Pomo were pushed off their land and onto reservations. Decimated by massacres and disease, by the 1870s only 10 percent of the original Pomo population remained.

"Pomo Indian Basket Weavers: Their Baskets and the Art Market," organized by the University of Pennsylvania Museum of Archaeology and Anthropology, ably demonstrates the incredible economic transformation that overtook the remaining Pomo as they adapted to life in white, 20th-century California. What originally was a utilitarian craft used in everyday life gradually became a cottage industry producing fine art for sale to dealers and collectors.

At the turn of the century, a popular mania for Indian arts and crafts made Pomo baskets especially in demand. While a male Pomo could earn $20 a month as a ranch hand around 1900, his wife could net $15 a week creating baskets. The tourist market for decorative coiled and twined ones in traditional designs was hot.

The exhibition concentrates on about 40 individual makers from 1890 to 1920 through historical photographs as well as 125 extraordinary woven and patterned baskets. Several videotapes show contemporary Pomo describing what the making of baskets was like then and now.

Most of the baskets have geometric designs in light and dark browns. Figures are usually not shown, but one large basket by Polly Holmes from ca. 1904-06 has pairs of figures and linked diamonds with checkerboard patterns. It also has clamshell beads intermittently around the rim and a few black quail topknots.

Miniature baskets that would fit on the tip of your finger are one spectacular kind of Pomo Indian basket. Another is "sky baskets," woven baskets partially or totally adorned with tiny feathers, clamshell and abalone beads.

A coiled and feathered masterpiece by Mary John Posh, dating from around 1905, took 11 months to complete. Less than a foot in diameter, the underside is aswirl in concentric red circles formed by the crest feathers of 233 woodpeckers with the outermost circle composed of the black plumes of 250 quail. Edged in tiny circular flat beads of clamshell, 32 ornaments of four more clamshell beads ending in arrow-like pieces of abalone shell dangle in two rows amid the field of red feathers.

Baskets were made traditionally by women, but by the late 19th century a few men joined them. Mary Benson and her husband, for example, are represented by a basket in light-and-dark design with more than 100 stitches per inch. It took similar technical skill to weave the popular miniature baskets. The tiniest example on display is by Mary Poney Elgin, and dates from around 1906.You would need a magnifying glass to fully appreciate the design, as more than one would be needed to fill a thimble.

Distinctive Pomo forms include a basketry tray, a small mush basket (for the Pomo's traditional staple food, acorn mush), an oblong boat basket (all the men fished), huge round feast baskets and large, cone-shaped burden baskets.

The "sky baskets" with their glorious feathers, like the one by an unknown maker that shimmers with iridescent green feathers trimmed in black quail plumes, were symbolic of Pomo creation concepts. Birds' feathers would wing to the spirit world and abalone shells reflect the gleam of the stars. Makers would fast before starting a basket to purify their minds. Much of the original symbolism has been lost for sky baskets, as has the meaning behind most of the other designs.

The remaining Pomo, members of 72 related tribes, banded together to buy back their land from the 1870s onwards. Today 17 federally recognized communities and one independent Pomoan tribe live in northern California. Only about 30 weavers are active. After the Depression collapsed the market for their wares, environmental degradation has gradually reduced the pristine marshy areas needed to produce the willow shoots, sedge, bulrush, redbud, shells and feathers necessary to create baskets. And it is difficult to make a profit from an enterprise that requires many months of preparing materials before the basket itself is even started.

Baskets from three generations are displayed to show how designs evolved, and photographs of the makers create a feeling of intimacy. These early Pomo baskets are an important legacy, and the exhibition acknowledges both their makers and the caring collectors who kept track of the artists behind these stunning artworks.

Regrettably, the show has no catalogue. But a special issue of Expedition magazine (from which several images for this review were taken) dedicated to "Pomo Indian Basket Weavers" is available at the museum shop for $9.50.