California utility companies are continuing their mad rush to achieve the Golden State’s mandate requiring 20 percent of their electricity be generated from solar, wind or other renewable sources by 2010.

Southern California Edison, an Edison International company, is the latest to strike a clean-energy deal. On Monday the Rosemead, Calif.-based utility, which provides power to 13 million people, said that it signed a 20-year contract to get up to 909 megawatts of wind power from DCE, an affiliate of Caithness Energy.

The project, called Caithness Shephard’s Flat, is expected to generate 2 billion kilowatt-hours per year of renewable energy by 2012. It will involve the installation of 303 wind turbines across a 30-square-mile section of Oregon. Edison said once completed it will be one of the world’s largest wind farms.

The announcement comes just four days after Pacific Gas & Electric, the major utility in Northern California, announced two solar power contracts totaling 800 megawatts of renewable energy. Topaz Solar Farms, a subsidiary of OptiSolar, will provide the San Francisco-based utility with 550 megawatts of power from thin-film photovoltaic installations.

Pacific Gas & Electric also signed a contract with High Plains Ranch II, a subsidiary of SunPower Corporation, for 250 megawatts of photovoltaic solar power.

California’s third major utility, San Diego Gas & Electric, has also been busy chasing clean energy. In July it announced plans to develop between 70 and 80 megawatts of solar electricity. Small change compared with the bigger announcements by its brethren to the north, but every bit of renewable energy counts in the race to 20 by 10.