Sierra concerns a group of young gung-ho rangers at the fictitious Sierra National Park. Yosemite National Park, California — mountainous terrain with sheer, rugged cliffs, huge cascading waterfalls, towering majestic sequoias—is the principal setting for "'Sierra.'" Weekly series dramatizing the exploits of the National Park Service Rangers. Starring in the series are James G. Richardson as Ranger Tim Cassidy, Ernest Thompson as Ranger Matt Harper, Jack Hogan as Chief Ranger Jack Moore, Mike Warren as Ranger P. J. Lewis and Susan Foster as Ranger Julie Beck. The safety and well-being of the thousands of visitors who are lured every week of the year to this 758.870 acres of incredible beauty, is part of the responsibility of these dedicated men and women. Filmed in cooperation with the National Park Service. The rangers work in a world of constant change, as varied as the weather, the animals and the people who visit the park system. Some situations are terrifying and some are humorous. Campers, hikers, skiers, climbers — some friendly, some fun-loving, some stub-born, some cruel — create different challenges each day for the confident and skilled rangers.