Before lighthouses, mariners sailing along the rugged west coast anchored their ships at night rather than risk disaster in darkness. Beginning in the 1850s, the U.S. Light-House Service built a string of lighthouses along the west coast that marked geographic locations and guided ships safely, much like illuminated mileposts on a dark highway. These lights opened the ocean route to nighttime commerce and encouraged settlement of the Pacific Northwest. By 1897, the lighthouses of Oregon and Washington were spaced so mariners could usually see the next light before losing sight of the previous beacon, using lamp color and flashing patterns to distinguish them. Large coastal lights such as Yaquina Head Lighthouse helped create an ocean highway, while smaller harbor lights including Yaquina Bay Lighthouse marked its exits. A first-order Fresnel lens made the Yaquina Head light visible 20 miles away; it first showed a fixed white light, and in 1939 the U.S. Coast Guard assigned its current flashing pattern to distinguish it from other lighthouses.