The Choluteca River, which crosses the city from south to north, physically separates Tegucigalpa and Comayagüela.  El Picacho Hill, a rugged mountain of moderate height, rises above the downtown area; several neighborhoods, both upscale residential and lower income, are located on its slopes. The city consists of gentle hills, and the ring of mountains surrounding the city tends to trap pollution. During the dry season, a dense cloud of smog lingers in the basin until the first rains fall.