The saloon that old-timers claim once stood on the island's high ground has vanished, allegedly washed away by the great flood of 1894. Also gone are the fishwheels, the water-driven devices whose rotating baskets scooped salmon from the majestic Columbia River. What remains are the shady woodlands of black cottonwood, willow and ash and the insects that gave The Nature Conservancy's 85-acre Pierce Island Preserve its original name—Mosquito Island.

Pierce Island is underlain by cobble and coarse gravel, reportedly deposited after impounded river waters broke through the Table Mountain landslide deposit of basalt rock that had temporarily dammed the Columbia 1,200 years ago. Overlying this cobble and gravel are more recent deposits of finer gravels, sands and silts.

Because humans played a relatively small part in the island's long history, Pierce is considered among the best remaining natural islands in the Columbia River Gorge. It is one of the few in the region that has not been significantly altered by conversion to other uses. However, in the early 1980s even this island was threatened by a proposal to clear-cut its forest to create a disposal site for dredge spoils from the construction of the Bonneville Dam.

Transforming Pierce Island into a dredge disposal site would have meant the loss of an important river floodplain, including nesting and overwintering habitat for the Great Basin subspecies of Canada goose. Other animal inhabitants, including great blue heron, osprey and beaver would also have suffered from the destruction of the island's habitats.

In addition, a population of a rare-plant species would have been jeopardized. Persistent sepal yellowcress (a member of the mustard family) grows on the island's cobble-gravel shoreline. Fewer than a dozen locations are known for this species in all of North America, and only one—Pierce Island—offers the plant any formal protection.

In 1984, the Conservancy bought the island from the Knappton Corporation, a marine transportation company headquartered in Portland, Oregon. The preserve and its adjoining shorelands, which comprise as much as 200 acres when the water level of the Columbia is low, now lie within the federal Columbia Gorge Scenic Area. Situated in one of the last major free-flowing stretches of the Columbia River, Pierce Island offers spectacular views of the Columbia Gorge and Beacon Rock.