Marsh Creek State Historic Park is a California state park in east Contra Costa County, California, United States. It was named as the newest California State Park on January 27, 2012. The newly named park (formerly called the Cowell Ranch/John Marsh State Park) contains 3,659 acres (1,481 ha; 5.717 sq mi) and is about 3.3 miles (5.3 km) south of downtown Brentwood.
The park is named for California pioneer John Marsh (1799–1856), who was a doctor, rancher, landowner and the first non-Hispanic European to settle in what is now Contra Costa County, California. Marsh was the first medical doctor in California, the first Harvard graduate in the territory, the first to introduce a number of new crops, and one of the most influential men in the establishment of California statehood.Marsh, a widower, was a native of Massachusetts, who had previously lived in Minnesota, Illinois, Wisconsin, Missouri and New Mexico before settling in Los Angeles, California. In 1838, he acquired Rancho Los Meganos in northern California. The ranch covered over 80 square miles (21,000 ha), and extended over 8 miles (13 km) to the San Joaquin River, where Marsh's Landing was built (near present-day Antioch, California). The park covers a portion of this former rancho. Marsh reportedly paid $300 in cowhides for the land. The John Marsh House was added to the National Register of Historic Places (Reference Number 71000136) under Criteria A, B and C on October 7, 1971.The park is significant for many reasons. It represents the Mexican period in California history, it was an important site for the Miwok and other Native American people, it was home of the vaqueros, it was the end point of the California Trail (the first party over the Sierra Nevada came directly to the John Marsh rancho at his invitation), and its archaeological site has produced artifacts going back 7,000 years. It has been identified by the Sacramento Archaeological Society as being the most important archaeological site in the California State Park system.