Indiana Dunes National Lakeshore is a treasure of diverse natural resources located within an urban setting. The park is comprised of over 15,000 acres of dunes, oak savannas, swamps, bogs, marshes, prairies, rivers, and forests. It contains 15 miles of Lake Michigan shoreline spanning the distance from Gary to Michigan City. Immediately inland from the beaches, sand dunes rise to almost 200 feet in a series of ridges, blowouts, and valleys. The national lakeshore preserves an important remnant of a once vast and unique environment, resulting from the retreat of the last great continental glacier some 14,000 years ago. The park landscape represents at least four major successive stages of historic Lake Michigan shorelines, making it one of the most extensive geologic records of one of the world's largest, freshwater bodies. Over 1,100 flowering plant species and ferns make their homes here. From predacious bog plants to native prairie grasses and from towering white pines to rare algal species, the plant diversity is rich. The park is also renowned for its bird life; more than 350 species have been observed here.