Native prairies are among the most endangered ecological communities in North America. Western Washington is generally known for its forests; it is less well known that the south Puget Sound area historically had large expanses of prairie and oak savannahs. These prairies and woodland communities developed during a warm dry period from 10,000 to 7,000 years ago on the droughty, gravelly soils deposited by the Vashon Glacier. In the recent past, glacial outwash prairie still existed on at least 150,000 ac, and grassland and oak woodlands occurred in smaller patches throughout the Puget Trough and south to the Columbia River. Local Native American tribes adapted to use the plants and game of these communities and maintained prairie in the area by burning the vegetation every few years during the last 4,000 years. Since settlement by Euro-Americans, the extent of these prairies has steadily declined with their use for agriculture and the cessation of burning that has allowed succession to Douglas-fir forest. Only about 8% of the original prairie still supports grassland vegetation and about 2-3% is still dominated by native prairie vegetation. In addition to prairies on glacial outwash, native grasslands existed on perhaps 10,000 ac of coastal headlands, islands and rocky balds. Some of the wildlife of prairies, though now locally rare, are little different from abundant and widespread forms found across much of eastern Washington and in grassland communities elsewhere. A few of the wildlife species that inhabited these prairies and grasslands have been genetically isolated from their ancestral stocks for a long period of time and have evolved endemic forms found nowhere else. These unique forms have become rare with their habitat, and some are threatened with extinction. This report summarizes what is known about the natural history and status of three species that have their center of abundance in Washington on the prairies of the southern Puget Sound: the Mazama pocket gopher; streaked horned lark; and Taylor’s checkerspot butterfly.