and northeast of San Antonio. Austin occupies a total area of . Approximately of this area is water. Austin is situated at the foot of the Balcones Escarpment, on the Colorado River, with three artificial lakes within the city limits: Lady Bird Lake (formerly known as Town Lake), Lake Austin (both created by dams along the Colorado River), and Lake Walter E. Long that is partly used for cooling water for the Decker Power Plant. Mansfield Dam and the foot of Lake Travis are located within the city's limits. Lady Bird Lake, Lake Austin, and Lake Travis are each on the Colorado River. The elevation of Austin varies from to approximately above sea level. Due to the fact it straddles the Balcones Fault, much of the eastern part of the city is flat, with heavy clay and loam soils, whereas the western part and western suburbs consist of rolling hills on the edge of the Texas Hill Country. Because the hills to the west are primarily limestone rock with a thin covering of topsoil, portions of the city are frequently subjected to flash floods from the runoff caused by thunderstorms. To help control this runoff and to generate hydroelectric power, the Lower Colorado River Authority operates a series of dams that form the Texas Highland Lakes. The lakes also provide venues for boating, swimming, and other forms of recreation within several parks on the lake shores. Austin is located at the intersection of four major ecological regions, and is consequently a temperate-to-hot green oasis with a highly variable climate having some characteristics of the desert, the tropics, and a wetter climate. The area is very diverse ecologically and biologically, and is home to a variety of animals and plants. Notably, the area is home to many types of wildflowers that blossom throughout the year but especially in the spring. This includes the popular bluebonnets, some planted by "Lady Bird" Johnson, wife of former President Lyndon B. Johnson. The soils of Austin range from shallow, gravelly clay loams over limestone in the western outskirts to deep, fine sandy loams, silty clay loams, silty clays or clays in the city's eastern part. Some of the clays have pronounced shrink-swell properties and are difficult to work under most moisture conditions. Many of Austin's soils, especially the clay-rich types, are slightly to moderately alkaline and have free calcium carbonate. Cityscape Austin's skyline historically was