Eureka is the principal city of Humboldt County. The city is located on U.S. Route 101 on the shores of Humboldt Bay, 270 miles (430 km) north of San Francisco and 100 miles (160 km) south of the Oregon border. Greater Eureka, one of California's major commercial fishing ports, is the location of the largest deep-water port between San Francisco and Coos Bay, a stretch of about 500 miles (800 km). The headquarters of both the Six Rivers National Forest and the North Coast Redwoods District of the California State Parks System are in Eureka. As entrepôt for hundreds of lumber mills that once existed in the area, the city played a leading role in the historic West Coast lumber trade. The entire city is a state historic landmark, which has hundreds of significant Victorian homes, including the nationally-recognized Carson Mansion, and the city has retained its original 19th-century commercial core as a nationally recognized Old Town Historic District. Eureka is home to California's oldest zoo, the Sequoia Park Zoo.