Ryan Hydroelectric Facility, Ryan-to-Rainbow 100 kV Transmission Line, West bank of Missouri River, northeast of Great Falls, Great Falls, Cascade County, MT

Significance: The transmission line is an early and well preserved example of an important innovation in electric power transmission line technology, the H-frame support structure. Comprised of two-wood poles connected by a cross-arm(s), the H-frame offered a viable and comparatively economical means for the construction of transmission lines of over 66,000 volts. It became the standard for high voltage line construction following its introduction in the mid-1910s, and remained so for decades.
Survey number: HAER MT-98-C
Building/structure dates: 1915 Initial Construction