 Nevada is the third most seismically active state in the U.S. (after Alaska and California); the United States Geological Survey has estimated that over the next 50 years, Clark County has a 10–20% chance of a M6.0 or greater earthquake occurring within of Las Vegas.In 2000 there were 512,253 households out of which 31.70% had children under the age of 18 living with them, 48.70% were married couples living together, 11.80% had a female householder with no husband present, and 33.70% were non-families.24.50% of all households were made up of individuals and 6.70% had someone living alone who was above age 64.