The Gulf of Mexico and the Gulf Stream bracket the Florida Peninsula on the west and east. The lighter shade of blue in the Gulf of Mexico is due to the much shallower (continental shelf) water depths of less than 200 feet (60 meters), whereas the much darker blue of the Gulf Stream is due to water depths in excess of 2000 feet (610 meters). Tampa Bay and Charlotte Harbor are fairly large water embayments along the west coast, and Lake Okeechobee is the large body of water in the south-central part of the state. Numerous smaller lakes can also be seen generally extending north and south through the central part of the state. Practically all of the lakes in central Florida have been created by the interaction of water with the limestone rock that underlies most of the state. Thus, through time, sinkholes have developed, occasionally swallowing houses and roads as the limestone rock collapses. This type of topography is termed karst. Visible along the southeastern coast of Florida is a large urban area that stretches roughly from Homestead in the south to beyond West Palm Beach in the north (including the greater Miami area). This built-up area is known as the Gold Coast of Florida. To the west of this vibrant and ever-growing urban area is the vast, relatively uniform-looking swampland of the Everglades, which is virtually uninhabited by humans. In fact, most of the flat, saw grass landscape is occasionally interrupted by small stands of hardwood hammocks; this area is part of the Big Cypress National Preserve and the Everglades National Park. Most of the Florida Keys are visible as they form an archipelago that arcs to the southwest from the southern tip of Florida. Also visible are parallel lines of clouds that have been formed as a cool air mass from the northwest is pushed across the warmer water of the Gulf Stream. A very faint smoke plume that originates near the Georgia-South Carolina border provides a clue to the wind direction at the time this photograph was taken.