Southern Wyoming has served as a major travel corridor since the mid 1800s because emigrants traveling west needed safe routes with food and water, and guides familiar with the region determined that the best route crossed the basins of Wyoming north of the southern Rocky Mountains. Over the next century, emigrant trails, stagecoach routes, railroads, telegraph and telephone lines, and roadways were established along this corridor. From 1843 to 1869, more than 500,000 emigrants traveled westward across Wyoming on the Oregon, California, Mormon, Cherokee, and Overland Trails toward California, the Salt Lake Valley, and the Pacific Northwest. From 1860 to 1861, Pony Express riders carried mail in relay between St. Joseph, Missouri and Sacramento, California in only 10 days, changing horses at stations spaced about 10 miles apart along the 2,000-mile trail. In the early 1860s, the Pacific Telegraph Company ran its cross-country telegraph line through southern Wyoming, providing the only instantaneous communication link between the east and west coasts. From 1862 to 1868, the Overland Stage carried over 20,000 travelers a year, including Mark Twain and Horace Greeley, and for a time it was the only route on which the government allowed travel because of Indian conflicts on the Oregon Trail. In 1869, the transcontinental railroad crossed southern Wyoming to take advantage of the low grade and remain close to coal deposits used for fuel. In 1913, the Lincoln Highway became the first roadway to span the continent, later becoming US 30 within Wyoming in 1928 and evolving into I-80 during the 1960s and 1970s. In 1915, the first transcontinental telephone line followed the same path through Wyoming as the transcontinental railroad, and today fiber-optic cables carry modern telecommunications along this historic corridor. The red brick buildings distributed along I-80 are telephone line equalizer stations that clear, strengthen, and direct telephone transmissions. In 1920, transcontinental airmail planes generally followed the Union Pacific Railroad route and refueled at Cheyenne, Rawlins, Rock Springs, and Evanston.