During Helena's early years, this toll road, originating at the head of Missouri River navigation at Fort Benton, was the main shipping route into the area. Heavy rain and snow sometimes made the canyon road impassable.

In 1865, the Territorial Legislature granted a license to the Little Prickly Pear Wagon Road Company to build a toll road through the canyon. A year later, in 1866, Helena merchants James King and Warren Gillette bought the road and spent $40,000 upgrading it. By then traffic on it between Fort Benton and Helena had become so heavy, that the men were able to recoup their expenditure within two years.

By the early 1870s, it was part of the Benton Road, an important freight and passenger route in the territory. Thereafter, other roads and a railroad were constructed through the Prickly Pear Canyon.

A section of the stagecoach road from Corinne, Utah to Helena, crossing the Beaverhead River at Point of Rocks, halfway between Dillon and Twin Bridges, 1871.

Corinne was founded in 1869 as a freight-transfer point on the new Union Pacific Railway line for the shipment of goods and supplies to the mining towns of western Montana along the Montana Trail, the most important early-day land route.

Both the Benton Road and the Montana Trail were expensive and unreliable, so Helena merchants developed the Carroll Trail, named for one of the owners of the Diamond R freight company. Steve F. Russell of Historic Trails Research in Ames, Iowa, has written a concise history of the Carroll Trail (pdf file).

This about the Carroll Trail by Hal G. Strearns, writing in the 4/11/1977 Helena Independent Record:

"In 1874 the Northern Pacific had gotten as far as Bismarck and from there the boats
labored up to Carroll, some 75 miles east of Lewistown, about 30 miles upstream from the
mouth of the Musselshell. It was March 16, 1874 when the teamsters began trekking
from Helena to Carroll, working for the Diamond R Transportation Co, which belonged to
Col. Broadwater, Mathew Carroll, George Steele and E.G. Maclay. Their wagons could
make about 13 miles a day, a parade of teams two to three miles in length.

"The Carroll Trail followed the Helena valley to Clasoil, then via the present day Highway 284
to Canyon Ferry, through White's Gulch, over the Belts, to Fort Logan, Brewer's Hot
Springs, down the Musselshell, through the Judith Gap to Roy and to Carroll.

"Very little remains of Carroll, the river's waters having done in the famed port. And precious little is left of Fort Maginnis where troops were stationed to handle marauding Indians."