Basin is an unincorporated community and census-designated place (CDP) in Jefferson County, Montana, United States.

Named for the many large boulders in the vicinity, the town of Boulder Valley was established in the early 1860s as a stagecoach station on the route between Fort Benton and Virginia City.[5] It later became a trading center for nearby agricultural areas and the Elkhorn,

Amazon was a mining town that got its start in the 1880's. Silver was discovered in the area in 1872 and by 1883 a concentrator was located here. The railroad tunnel, constructed by the Montana Central Railway (part of the Great Northern), was cut by 1888 (the first train passed through on October 25, 1888), connecting Amazon to the smelters at Wickes and East Helena. However, the mining slowed considerably at Amazon by the late-1880's and did not pick up again until about 1903. By 1953, all the mines in the area were closed.

In 1887, construction on the tunnel began. Crews worked from both ends. The north end was called Portal and the south end Amazon. When the tunnel was built, it was the longest railroad tunnel in Montana at 6,145 feet. The first train rolled through the tunnel on October 24, 1888.

The large wooden doors were added at each end and kept closed in winter to keep snowdrifts out and the warm air in. These doors had to be opened every time a train passed through and needed to be closed afterward.

Alhambra was a resort town situated South of Helena and relied on the heavy traffic during the golden days of mining in the area. Alhambra and Sunnyside Hot Springs were the two hotels in the town, together composing a medical and recreational resort that flourished in the 1860s until the 1950s. Alhambra Hot Springs consists of four main springs and a number of hot water seeps located along Warm Springs Creek. The water temperature averages 138 degrees F. and is slightly radioactive.