Of the 15 National Forests in the Northern Region of the USDA Forest Service, the Lolo National Forest is estimated to be the third largest. It is located in western Montana. Several major tributaries to the Clark Fork River of the Columbia River Basin flow through the Forest. Although its 2.1 million acres of diverse and spectacular mountainous country extend into seven counties, the Lolo National Forest is primarily located in Missoula, Mineral, and Sanders Counties, providing an important stimulus to the area's economy, recreation, and esthetics.