San Francisco covers an area of about 46.89 square miles (121.4 km2), making it the second most densely populated large U.S. city, and the fifth most densely populated U.S. county, behind only four of the five New York City boroughs. San Francisco was founded in 1776, however three-quarters of the city was destroyed by the 1906 earthquake and fire and rebuilt. San Francisco is also the headquarters of companies such as Fitbit, Salesforce.com, Airbnb, Pacific Gas and Electric Company, and Uber.