Shreveport is the southernmost post-bubble city. It got its start and its name from a captain in the US Corps of Engineers, who figured out how to clear the Red River of a natural logjam 180 miles long and bring shipping to a juncture with an overland route to Texas. In the Civil War, it suffered less than other parts of the confederacy and its troops actually surrendered weeks after Robert E. Lee did. In the housing bubble, Shreveport and Bossier City across the river have escaped essentially unscathed. Housing prices have risen steadily – from $135,600 in 2007 to $155,900 in the second quarter of 2010, a 15 percent increase. Although the metropolitan area has the lowest median household income of the six post-bubble cities, its population has been stable (after a temporary influx from hurricane Katrina). Employment is the highest its been in a year, helped by the area's largest employers: Barksdale Air Force Base in Bossier, Louisiana State Medical Center, and several casinos. The biggest change is the move by several natural gas-drilling companies to lease land for wells to tap the area's Haynesville Shale, a shale-rock formation that may contain the largest natural gas field in the continental United States.