More than 140 houses in Gainesville were built using the limestone rocks, called chert, that were abundant in the quarries of North Florida between 1920 and 1940. Builders first turned to the material during the Florida land bust in the late-1920s and it saw widespread use during the Great Depression through World War II. Its use declined after the war, but by then it had already become a recognizable part of the city and builders still periodically use it as an architectural embellishment. Chert houses are found all over the city, but in Historic Gainesville, most are located in five neighborhoods - College Park, Hibiscus Park, Golfview Estates, University Heights North and University Heights South. The City of Gainesvilles Historic Preservation Division is pushing to have these homes protected by creating historic districts. Regulations in historic districts require houses that have been designated as "historically contributing" to get certificates approving major construction that could damage the integrity of history.