Five miles northwest lies the geographic center of Texas, an imaginary point whose coordinates divide the state into four equal areas. In straight-line distance it is 437 miles from the state's most westerly point on the Rio Grande River above El Paso, 412 miles from the most northerly point in the northwest corner of the Panhandle near Texline, 401 miles from the most southerly point on the Rio Grande below Brownsville, and 341 miles from the most easterly point on the Sabine River near Burkeville. Texas reaches a maximum border-to-border distance of 801 miles from north to south and 773 miles from east to west. Within the state's 4,137-mile perimeter are 267,339 square miles, or 7.4 percent of the nation's total area. Fifteen of the 50 states could fit within Texas' borders with more than 1,000 square miles left over. Brewster County in southwest Texas, with 6,208 square miles, is the state's largest county and larger than Connecticut, while Rockwall County in northeast Texas, with 147 square miles, is the smallest. Elevations rise from sea level along the 624-mile Gulf of Mexico coast to 8,751 feet at Guadalupe Peak in the Guadalupe Mountains, while altitude at this point is 1,545 feet. Texas terrain ranges from the subtropic Rio Grande Valley to the Great Plains, from the forests of east Texas to the rugged Trans-Pecos region, where mountain ranges thrust 90 peaks a mile or more into the sky, and its average annual rainfall ranges from more than 56 inches along the Sabine River to less than 8 inches in the extreme west.