Yellowstone's South entrance is only about a 1.75 hour drive from Star Valley and the west enterance is about 2.5 hour drive. Either way you have a scenic drive past the Grand Teton mountain range. I recomend going in one way and coming out the other.

Established on March 1, 1872, Yellowstone National Park is the first and oldest national park in the world.
Preserved within Yellowstone are Old Faithful Geyser and some 10,000 hot springs and geysers, the majority of the planet's total. These geothermal wonders are evidence of one of the world's largest active volcanoes; its last eruption created a crater or caldera that spans almost half of the park.

An outstanding mountain wildland with clean water and air, Yellowstone is home of the grizzly bear and wolf, and free-ranging herds of bison and elk. It is the core of the Greater Yellowstone Ecosystem, one of the largest intact temperate zone ecosystems remaining on the planet.
The human history of the park dates back 12,000 years. The events of the last 130 years of park history are reflected in the historic structures and sites associated with various periods of park administration and visitor facilities development.

Grand Teton National Park is a Scenic 60 minutes away. Established in 1929, Grand Teton National Park emerged from a complicated and controversial series of events. The park first consisted of the mountain range and several glacial lakes. Later the valley floor was protected as Jackson Hole National Monument. The two areas were combined in 1950.

Today the park encompasses nearly 310,000 acres and protects the Teton Range, Jackson Hole (mountain valley), a 50-mile portion of the Snake River, seven morainal lakes, over 100 backcountry and alpine lakes, and a wide range of wildlife and plant species.
The park is also rich in a cultural history that includes seven eras of human history: early peoples (paleo-indians), Native Americans (modern tribes), fur trappers, homesteaders, ranchers/farmers, conservationists, and recreationalists. Climbing, hiking and backpacking, camping, fishing, wildlife and bird watching, horseback riding, boating on Jackson and Jenny Lakes, rafting on the Snake River, bicycling, and photography are all common activities in the area.

About 4 million visitors enjoy the park each year, most visit between Memorial Day Weekend and Labor Day.

The South Fork of the Snake is in southeastern Idaho close to the Wyoming border. The South Fork begins as it flows out of 20 mile long Palisades Reservoir in the community of Swan Valley, forming a 64-mile stretch of legendary tail-water fly-fishing, it has been rated as the best wild trout fishery in the lower 48 states.The South Fork is also a beautiful river for flat water rafting, canoeing and kayaking. If you float this river in a canoe know what you are doing as it is big water and its flat-water appearance can fool you to its dangers.