During most of the nineteenth century and the early years of the twentieth numerous railroads were built throughout America. Some. grew into gigantic systems with names we recognize today; Southern Pacific, Atchison, Topeka & Santa Fe, Chesapeake & Ohio. Others faded into oblivion. But all, successful or not, were built to fill transportation needs. In Tuolumne County, California, located along the Mother. Lode and stretching into the high Sierra Nevada, the first railroad reached the county in 1897. By World War I a number of rail lines had been built. Several, having served their purpose, had already been removed by that time. They played varying roles in the different industries of the county; mining and minerals, lumber, hydroelectric power and agriculture, as well as passenger service. After the war many things changed. Automobiles and trucks successfully competed for some traffic. Mining suffered as labor costs increased while gold held at a price fixed by the government. Dams built by public agencies dwarfed the earlier projects of private industry. And, outside capitalists acquired control of companies that had formerly been locally owned and managed. The transportation picture changed dramatically from what: it had been before the war. The purpose of this paper is to study those early years of the twentieth century in Tuolumne County. What were the needs for railroads in different: industries and enterprises in the county between 1897 and 1917; and what was their importance to those industries? And finally what was the impact of railroads on the economic development of Tuolumne County as a whole? By focusing on an area with a relatively self-contained railroad network it is hoped that influences in the economy will be more apparent. Trends identified here should find application in other areas. It is also hoped that topics for future research will be suggested and that methods and resources for that research will be suggested.