High Island is the surface expression of a salt dome at the edge of the Gulf of Mexico. A thick layer of ancient salt exists throughout southeast Texas about 30,000 feet below the surface. At some location, like High Island, a column of salt was squeezed upward toward the surface. This “dome,” therefore, is a salt cylinder some six miles tall and about a mile in diameter. High Island rises 32 feet above the surrounding marshes, providing soil conditions favorable to trees and shrubs. It forms a unique and important island of habitat for migrating birds.