Sep. 30--Thursday will mark the first of a series of important 100-year anniversaries for the Valley and the state of Arizona.

Oct. 1, 1909, was the day electric power started being delivered to the Valley on a regular basis from the still-incomplete Theodore Roosevelt Dam on the Salt River.

That was followed by completion of the dam in 1911 and statehood in 1912 in a logical sequence of events that started Arizona on its 100-year path to prominence.

In the beginning, the dam, which was operated by the U.S. Reclamation Service until 1917 when SRP took it over, had a grand total of six electric customers. Today, SRP has 930,000.

The dam was able to produce power even before it was finished because power lines and the powerhouse at the base of the structure were completed, and the dam was high enough to create a reservoir behind it, said Shelly Dudley, senior historical analyst at SRP. "The power production was mainly to (water) pumps in the Valley, to cotton gins and a few manufacturing plants and to Pacific Gas & Electric Co. of Phoenix," she said.

In its early days, SRP was primarily a wholesale supplier of electricity. PG&E of Phoenix, a forerunner of Arizona Public Service, passed the juice on to retail residential and business customers.

SRP didn't begin retail sales of electricity until 1928, when it sold power to customers in rural areas that another APS forerunner called Central Arizona Light and Power Co. didn't want to serve.

Roosevelt Dam initially was capable of producing 12 megawatts of electricity. Due to advances in technology, the dam today generates 36 megawatts, enough to serve about 8,100 houses. But that is a tiny portion of the total demand for electricity in the SRP service territory. In 2009, the four SRP dams on the Salt River will supply less than 4 percent of the project's total electric load, with most of the power coming from coal, nuclear and natural gas plants.

Today, SRP is viewed as primarily an electric utility, but in 1909 electricity was just a byproduct of its water conservation efforts -- a way to raise a little extra money to help repay the federal government for construction of the dam. Still, it was an important development, Dudley said. "That first power delivery ... helped set up power as the paying partner for the water reclamation project and establish Salt River Project as the first multipurpose reclamation project," she said.

The story of Roosevelt Dam dates back to the late 1880s, when early surveying parties identified the site at the junction of the Salt River and Tonto Creek as an ideal dam location.