Here are links to other sites dedicated to remembering lost ski areas:
NELSAP, the New England lost ski areas project. To my knowledge, the earliest attempt to catalog and remember the places where people grew up skiing. Started in 1989(?), it covers the New England states of Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, and Connecticut. It also lists some areas in New York, New Jersey, Pennsylvania, Quebec, Alberta, and Afghanistan.
DC Lost Ski Areas lists lost areas in Pennsylvania, Maryland, Virginia, North Carolina, and West Virginia.
Colorado Ski History, has a section devoted to lost ski areas in Colorado. They also list a few in Utah, Wyoming, and one in Montana.
Lost ski areas of Washington has moved to wikispaces as Lost Ski areas of the Pacific Northwest. They cover Washington, Oregon, and Idaho.
California Ski Library doesn’t yet (see comment below) deal specifically with lost ski areas, but has a lot of information about the history of the sport in that state.