The second largest of the Northern Channel Islands, Santa Rosa Island is made up of over 52,000 acres and is located about 27 miles off the coast of Santa Barbara. Most of the island is made up of hills and grasslands, with some high mountains and deep canyons. The northeastern shore of the island is made up of terraces and cliffs, and sandy beaches abound there as well as on the northwest and southwest shores. With hundreds of different native and introduced plants on the island, there are many different biomes on the island including marsh, chaparral, coastal, forest, and woodland communities. Along with the many plants on Santa Rosa, there also exists a stand of Torrey pines on the northeast part of the island, with the only other natural occurance on the southern Californian coast in San Diego County. The endemic island fox, spotted skunk, seals, sea lions, and sea birds live in these many biomes, as well as many cattle as part of the ranching operations that continue there.

There are many archeological and paleontological sites on the island, with some dating back as late as 11,000 years ago. Santa Rosa Island is also the site of the finding of the world's most complete skeleton of the pygmy mammoth. Found in 1994, this dwarf species is related to the Columbian mammoths, and more sites are being found. Known as Wi'ma by the natives, Santa Rosa Island maintained a number of medium-size villages, the majority of which were concentrated on the northern side of the island. The island contains numerous deposits of igneous rock, which the natives used to make tools such as spearheads and drills. As with all the islands, the natives traded extensively with mainland, offering tools, beads, fish, sea lion meat, shells and sea otter skins for things unavailable on the islands. Two notable shipwreck sites can also be found on the island of Santa Rosa: the wreck of the S. S. Chickasaw near South Point, and the Goldenhorn wreck near Sandy Point. The first written record of Santa Rosa Island was in the journal of Juan Rodriguez Cabrillo, who called the island Nicalque. As with the other eight islands, the current name of Santa Rosa was standardized by George Vancouver in 1793.