Over a century ago, Los Angeles opened the floodgates on an engineering feat that ferried Sierra water along a 233-mile aqueduct to the San Fernando Valley. To be a great city, however, L.A. would need more juice.

On March 18, 1917, an operating engineer in a remote mountain canyon nearly 50 miles northwest of Los Angeles flipped a switch at the city’s first publicly owned commercial powerhouse.

San Francisquito Power Plant No. 1, a hydroelectric marvel along the L.A. Aqueduct above Saugus, sent a jolt of electricity toward a power hungry downtown — and energized a century of Los Angeles growth and progress.

“It’s really cool. It’s our first power plant,” declared Edward Lewis, an electrical service manager and a 34-year veteran of the Los Angeles Department of Water and Power, beaming among the hum of four large generators. “Los Angeles was in dire need of water and power.

“This plant signified the power that allowed Los Angeles to grow to the great city that it is.”

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Located high up rugged San Francisquito Canyon along a former Butterfield stage route lined with lush oak and pine, the monolithic power plant cut with long vertical case windows operates nearly unchanged from when it began a century ago.

Owens Valley water flows 940 feet down a hill through three penstocks into the back of the cavernous peach-colored building, turning Pelton water wheels that drive four generators, including one that dates back 100 years.

The discharge water then falls from tunnels at the base into a glistening pool.

Just down the road along a bubbling creek stands Pelton, an LADWP village of Craftsman-style bungalows that served workers and mule skinners for the L.A. Aqueduct and plant.

“Power Plant 1 is momentous. It’s wonderful,” said Matthew Coolidge, program manager for The Center for Land Use and Interpretation in Palms, who has visited and toured the facility. “It feels like it’s from another time. Yet it’s still doing its thing.”

Scroll back 100 years.

• RELATED STORY: 100 Years of Water: Los Angeles Aqueduct, William Mulholland helped create modern L.A.

Southern California and its City of Angels began to boom thanks to Southern Pacific and Santa Fe rail lines, newly found oil, a vast citrus empire and the promise of eternal sun.

At its center was the Spanish pueblo of Los Angeles, a small pile of bricks whose population had doubled to 100,000 in the decade leading up to 1900, then tripled to more than 300,000 people 10 years later, and nearly doubled again by 1920.

To expand, what the dry region desperately needed was water.

Chief Engineer William Mulholland would supply the Owens River water on Nov. 5, 1913, in Sylmar during a “There it is, take it” opening of the L.A. Aqueduct, then considered one of the monumental achievements of all the ages.

Chief Electrical Engineer Ezra F. Scattergood, a former New Jersey farmboy and the “father of municipal power” in Los Angeles, would supply the power.

He first built hydroelectric plants to help build the aqueduct, according to an LADWP L.A. Aqueduct centennial tribute. Then four plants along the gravity-fed waterway with enough juice for the city itself, adding up to 200 horsepower, or roughly 150 megawatts, with transmission lines to sell power to Pasadena.

“This is destined to be of immense value as a reliable source of hydro-electric power, which may be developed and supplied at a very low cost, thus assuring low rates to electricity consumers and serving an important part in the encouragement of industry,” said Municipal Engineering magazine published soon after the plant opened a century ago.

After six years of construction, San Francisquito Power Plant No. 1 opened at 3:15 p.m., during a ceremony crowded by Model Ts. An operator named P.J. Vogel flipped a switch, cranking out 200 kilowatts from a single generator.

The power coursing through a 115,000-volt transmission line toward Los Angeles would put the P into the city’s fledgling Bureau of Power and Light — and its later successor, the LADWP.

It was also enough to light up Highland Park-Garvanza neighborhood and East Los Angeles, and illuminate 1,100 streetlights, according to an LADWP brochure commemorating its 50th anniversary.

Two more generating units were installed the following April, enough to power roughly 20,000 homes, according to the DWP. Two more were added by 1928 — generating as much as 92,000 hp, or nearly 72,900 kw. A 1982 makeover consolidated two vintage generating units, bringing the current total to four.

With the city’s purchase of private power companies and an Edison distribution system, its power over the power within the city — made possible by the aqueduct and power stations from Boulder Dam to across the West — was complete.

The American entry into World War 1 on April 6, 1917, would hike the price of fuel oil, making hydroelectric power even more desirable.

“The DWP is special,” said former Councilman Tom LaBonge, a big booster for Los Angeles. “Over 100 years ago, its engineers (and workers) built something that still works for the people of Los Angeles.”

On March 12, 1928, the St. Francis Dam burst below Power Plant 1, hurling 12 billion gallons 54 miles toward the sea, destroying the city’s second power plant. At least 450 residents died in the 180-foot tall water rampage.

On May 30, 2013, a Powerhouse fire ignited near the plant, burning 24 homes and torching 30,000 acres across the Sierra Pelona Mountains.

On a recent day, Juan Morales, a DWP worker, brushed white paint across a clapboard DWP bungalow near the plant. Told of its centennial, he gasped in wonder.

“I’m proud to be working at this place,” he said, pausing within sight of displays of antique aqueduct and power plant equipment in a nearby exhibit and park. “Very proud.”