The lower Bull Run River changed dramatically in 1906, when the Mount Hood Railway and Power Company (MHR&P) began work on the Bull Run Hydroelectric Project.
The project included a powerhouse on the Bull Run River at RM 1.5 (RK 2.4), and a diversion dam on one of its largest tributaries, the Little Sandy River, 1.7 miles (2.7 km) from its confluence with the Bull Run River.
Water from the Little Sandy Dam diverted much of the Little Sandy's flow through a wooden flume about 3.2 miles (5.1 km) long to a 140-acre (0.57 km²) reservoir called Roslyn Lake and from there to the powerhouse.

To begin the project, the MHR&P needed access to the powerhouse site.
At the time, it took three hours by stagecoach to reach Bull Run from an electric railway depot in Boring.
Roads in the area had to be planked to be usable during heavy rains.
Access improved in mid-1911, when the company finished construction on a 22-mile (35 km) railway line between the Montavilla neighborhood in east Portland and Bull Run.
In 1912, the year the powerhouse began generating electricity, the MHR&P merged with the Portland Railway, Light and Power Company, (PRL&P), which later modified the line for use by electric trolleys.

In 1913, the PRL&P, the predecessor of the electric utility company known as Portland General Electric (PGE), expanded the hydroelectric project by building Marmot Dam at RM 30 (RK 48) on the Sandy River, from which it diverted water through canals and tunnels, the longest of which was 4,690 feet (1,430 m), to the Little Sandy River upstream of the Little Sandy Dam.
This increased the maximum flow along the flume to Roslyn Lake from about 200 cubic feet per second (5.7 m³/s) to about 800 cubic feet per second (23 m³/s).
Since the combined flow entered the lower Bull Run River after leaving the powerhouse, the system altered the flows of three rivers.
In 1999, close to a century after the start of the project, PGE announced that it would remove the Marmot and Little Sandy dams and related equipment and close the 22-megawatt powerhouse because of costs associated with maintenance and fish protection.
 Marmot Dam was demolished in 2007 and the Little Sandy Dam in 2008, restoring natural flows to the Sandy and Little Sandy.

In 1982, work on the Portland Hydroelectric Project, unrelated to the Bull Run Hydroelectric Project, began generating electricity at powerhouses below the dams at Reservoirs 1 and 2 on the Bull Run River.
Portland sells the electricity from a 24-megawatt plant at Dam 1 and a 12-megawatt plant at Dam 2 to PGE, which operates and maintains the equipment.
PGE, a corporation with home offices in Portland, has many other sources of electricity, which it sells to customers in a 4,000-square-mile (10,000 km²) service area in the northern Willamette Valley.
The lower Bull Run River changed dramatically in 1906, when the Mount Hood Railway and Power Company (MHR&P) began work on the Bull Run Hydroelectric Project. The project included a powerhouse on the Bull Run River at RM 1.5 (RK 2.4), and a diversion dam on one of its largest tributaries, the Little Sandy River, 1.7 miles (2.7 km) from its confluence with the Bull Run River. Water from the Little Sandy Dam diverted much of the Little Sandy's flow through a wooden flume about 3.2 miles (5.1 km) long to a 140-acre (0.57 km²) reservoir called Roslyn Lake and from there to the powerhouse.
To begin the project, the MHR&P needed access to the powerhouse site. At the time, it took three hours by stagecoach to reach Bull Run from an electric railway depot in Boring. Roads in the area had to be planked to be usable during heavy rains. Access improved in mid-1911, when the company finished construction on a 22-mile (35 km) railway line between the Montavilla neighborhood in east Portland and Bull Run. In 1912, the year the powerhouse began generating electricity, the MHR&P merged with the Portland Railway, Light and Power Company, (PRL&P), which later modified the line for use by electric trolleys.
In 1913, the PRL&P, the predecessor of the electric utility company known as Portland General Electric (PGE), expanded the hydroelectric project by building Marmot Dam at RM 30 (RK 48) on the Sandy River, from which it diverted water through canals and tunnels, the longest of which was 4,690 feet (1,430 m), to the Little Sandy River upstream of the Little Sandy Dam. This increased the maximum flow along the flume to Roslyn Lake from about 200 cubic feet per second (5.7 m³/s) to about 800 cubic feet per second (23 m³/s). Since the combined flow entered the lower Bull Run River after leaving the powerhouse, the system altered the flows of three rivers. In 1999, close to a century after the start of the project, PGE announced that it would remove the Marmot and Little Sandy dams and related equipment and close the 22-megawatt powerhouse because of costs associated with maintenance and fish protection.  Marmot Dam was demolished in 2007 and the Little Sandy Dam in 2008, restoring natural flows to the Sandy and Little Sandy.
In 1982, work on the Portland Hydroelectric Project, unrelated to the Bull Run Hydroelectric Project, began generating electricity at powerhouses below the dams at Reservoirs 1 and 2 on the Bull Run River. Portland sells the electricity from a 24-megawatt plant at Dam 1 and a 12-megawatt plant at Dam 2 to PGE, which operates and maintains the equipment. PGE, a corporation with home offices in Portland, has many other sources of electricity, which it sells to customers in a 4,000-square-mile (10,000 km²) service area in the northern Willamette Valley.
Bull Run River (Oregon)