One of the last undeveloped regions of San Francisco Bay Area land - eastern Contra Costa County - is booming so much that a county supervisor has asked local cities to consider a temporary halt to residential growth. Eastern Contra Costa County, with its rich delta topsoil, is where the Central Valley meets the Bay Area. For years, agriculture was the main industry in this area east of Mount Diablo and south of the Sacramento River-San Joaquin River Delta. The region is made up of the local cities Pittsburg, Antioch, and Brentwood, as well as such unincorporated towns as Byron, Bethel Island, and Oakley. But few of the jobs and regional shopping centers are in the area, and commutes are long. The demand for affordable housing in the high-priced Bay Area market is one of the reasons behind the growth. "Homes are $200,000 less than in the central county or the San Ramon Valley," said Supervisor Joe Canciamilla, who recently proposed the moratorium and who represents the East County area. "A number of jurisdictions out there really want to grow," said John Landis, a professor of city and regional planning at the University of California, Berkeley. In addition, he said, cities like Antioch already have specific plans in place for growth, and large agricultural parcels in the area are attractive to developers. Growth figures tell the story in the East County. Brentwood, a town of 7,500 in 1980, has more than doubled in size since then. The city's general plan, adopted in 1993, calls for an eventual population of 79,000. Antioch grew from 42,683 to 74,900 between 1980 and 1995, a 75.5% increase. In contrast, Orinda, a slow-growth community in the western portion of the county, grew only 2.5% during that same period. In the east county, a total of 17,300 residential units have been approved but not built, and another 25,200 units are awaiting approval. The biggest development is Cowell Ranch, a 5,200-unit development proposed southwest of Brentwood, which may be annexed into the city if built. But the project appears to be on hold, according to Tom Mooers of the open space group Greenbelt Alliance. A vote on whether to incorporate the town of Oakley is on the November ballot. About 21,000 people currently live there, but the county's general plan called for the area to have a population of 50,000 by the year 2005. "People are really unsure what it (incorporation) means in terms of growth and development," Mooers said. But three developments in recent months could have long-term impacts on growth in the East County Region: o Supervisor Joe Canciamilla, who represents the East County, has called for a short-term moratorium on growth until a subregional plan is adopted. Traffic projections prepared by the Contra Costa Transportation Authority predict that within ten years, traffic congestion on Highway 4, the main traffic route in the East County, and other local arterial roads will exceed Level F, the lowest level of efficiency. The moratorium would probably last about a year. o In Byron, an unincorporated east county area north of Livermore, a Municipal Advisory Council recently released a master plan to deal with expected growth. The plan which identified 10,000 acres for residential development and 3,000 acres for commercial development, may never go into effect. That's because there is only five acres remaining within Byron's urban limit line, although growth may be allowed near the town's airport. o Preliminary discussions of an habitat conservation plan may preclude development on some East County land. The area is home to the San Joaquin kit fox, Alameda whip snake, California redlegged frog, California Tiger salamander, and vernal pool fairy shrimp. Only the kit fox is currently on the federal endangered species list. The other animals are either considered threatened or are candidate species for federal listing. Canciamilla said he envisions the subregional plan as working like a joint powers agreement. "It would have whatever force we agreed to," he said. The supervisor plans to meet with officials from each city to discuss his proposal, and hopes to produce a new plan by July 1999. The proposed moratorium would not affect commercial or industrial development, he said. The supervisor's plan meets with the approval of the county's Homebuilders Association. "In a sense, he's right," said Guy Bjerke, staff vice president. "Eastern Contra Costa needs to develop a strategic plan." Most large projects take over a year to win approval, Bjerke said, so it's hard to say if any projects would be affected by a slowdown. Only 1,700 housing units are built in the East County each year, he said, and 17,300 units have already been approved. Supervisor Canciamilla has also called for an update of the county's general plan. Among the items that need to be discussed, he said, are urban limit lines in the current plan that were adopted by voters in 1990. That same year, voters also agreed to a general plan that would urbanize only 35% of the county's unincorporated land. While a study is underway to determine how much of the county's unincorporated land is already urbanized, "potentially we're close to [the 35 % figure]," Canciamilla said. The supervisor said money doesn't exist for the traffic improvements needed for new developments in the East County. A subregional approach would force cities to look at the impacts of their decisions on a larger area. Canciamilla also has called for an agricultural and open space protection act to protect open space. Countywide, environmentalists have seen victories in recent months, which may translate to new policies for the East County. In one instance, developers withdrew plans for the 5,200-unit Tassajara Valley project proposed near Danville and San Ramon after public opposition. Because of the current anti-growth mood, county planners are advising developers not to invest in plans that the Board of Supervisors are likely to reject, according to the Contra Costa Times. Contacts: Supervisor Joe Canciamilla, (925) 427-8138. Winston Rhodes, associate planner for Brentwood, (925) 634-6905. Tom Mooers, East Bay Field Representative, Greenbelt Alliance, (925) 932-7776. Guy Bjerke, staff vice president, Homebuilders Association, (925) 820-7626. Bob Pine, senior fish and wildlife biologist, U.S. Fish and Wildlife Service, (916) 979-2728.