Returning for its fourth year, the Throckmorton Mountain Film Festival once again brings the great outdoors to the big screen in Mill Valley. Packing 55 new documentaries into three days, the Mountain Film Fest covers outdoor topics ranging from extreme sports to environmental activism. Special events include the opening-night party with festival filmmakers on hand, live music and a screening of the new documentary Unbranded, which follows a Texas cowboy training wild horses in even wilder terrain. The Mountain Film Festival takes place Friday to Sunday, Sept. 18-20, at Throckmorton Theatre, 142 Throckmorton Ave., Mill Valley. $14 per screening; $140 full pass. 415.383.9600.