Antelope Island State Park

Sources give the island's size as about 42 square miles (roughly 28,000 acres), around 15 miles long and 4.5 to 5 miles wide, though the figures vary slightly by source and with lake level. Utah State Parks says the island's oldest exposed rocks, the Farmington Canyon Complex gneiss, are about 1.7 billion years old, the same age as rocks at the bottom of the Grand Canyon; Wikipedia gives an older figure of about 2.7 billion years. The surrounding Great Salt Lake is the remnant of ancient Lake Bonneville.

Explorers John C. Frémont and Kit Carson visited in 1845 and killed a pronghorn there, which is the source of the island's name. In the late 1840s the Latter-day Saint church sent Fielding Garr to run a ranch for church livestock; the ranch house built in about 1848-49 still stands and is run as a historic site within the park. The state bought the northern part of the island in 1969 and the remainder, including the ranch, in the early 1980s. A northern causeway opened in 1969; floods washed out the causeways in 1983, and vehicles returned in 1993.

Twelve bison were bought in January 1893 by John Dooly and W. H. White and brought to the island in February 1893, according to Utah State Parks. The herd is now large enough to be managed with an annual fall roundup, which began in 1987 and in which animals are sorted, health-checked and some are sold. Park staff describe the herd as one of the country's largest and oldest public bison herds, and Wikipedia gives a current herd of roughly 550 to 700 animals. Other wildlife includes pronghorn, bighorn sheep, mule deer, coyotes and bobcats, and millions of birds use the lake's shorelines. Egg Island and White Rock Island are closed year-round to protect nesting birds.

The park describes hiking, mountain biking and horseback riding on backcountry trails, primitive camping, year-round interpretive programs, and swimming or floating in the lake's salty water at Bridger Bay Beach, where restrooms and showers are available. The island is a designated International Dark Sky Park. The Fielding Garr Ranch has a museum and exhibit.

Rideshare services such as Uber and Lyft do not pick up at the park, according to the state, which makes a private vehicle with a driver a practical option; Voyzo can collect your group door to door and drive you across the causeway. Park hours, roundup dates, water levels, boat ramps and access vary, so check Utah State Parks for current information.