County planners are grappling with how to manage rapid growth in western Pinal County without repeating the mistakes that turned San Tan Valley into what one commissioner bluntly called a “nightmare.”

During a work session Thursday, county development staff outlined the scale of what could be coming to areas such as Hidden Valley, Thunderbird Farms and Stanfield.

Planning Manager Harvey Krauss said roughly 15 previously approved developments in those areas remain unbuilt. If they all move forward, they would add about 54,000 dwelling units, housing an estimated 125,000 people.

That figure is nearly double the total number of residential lots currently inside Maricopa city limits, which has about 29,800. Krauss said many of the projects are designed with smaller lots and homes and resemble urban neighborhoods more than rural subdivisions.

“This is city-type development. The county doesn’t really provide urban services, we provide county services,” he said. Siena alone would bring more than 5,600 homes to the 1,400-acre area near Amarillo Valley Road and Louis Johnson Drive.

“This should be served by a municipality,” he said. “So, this whole area is going to be urbanized. It’s rural now, but it’s transitioning.”

Krauss emphasized that the pace of growth depends heavily on jobs and infrastructure.

“These houses will not come unless there’s employment … I’m not talking about retail, we’re talking about basic industry, there’s got to be jobs for people to be able to move into these houses to qualify for mortgages,” he said.

He cited employers such as Intel and Lucid, along with proposed data centers and energy projects, as examples of the type of industry that could drive housing demand.

“We’re going to see a lot more employment on the west side of Casa Grande, all the way to Maricopa,” he said. “I anticipate that… this will spur that type of [housing], like it or not.”

His recommendation was for the county to “grow smartly and responsibly” by “respecting private property rights but weighing the public interest.”

Some commissioners, however, questioned whether growth might arrive faster than planners expect.

Commissioner Karen Mooney, who represents San Tan Valley, noted that her area grew from about 60,000 residents to nearly 120,000 in roughly 15 years.

“What can be done differently so that other areas of Pinal County don’t end up like the nightmare called San Tan Valley?” she questioned. “Sorry, but a piece of Velcro was put on San Tan Valley and items were thrown, and where it stuck is where it went.”

Mooney pointed to the lack of commercial development in San Tan Valley and said proposed projects elsewhere appear poised to repeat that imbalance.

At Siena, developers are proposing to set aside just 45 of the 1,400 acres for commercial use. That represents about 3.2% of the site, roughly equivalent to two Southbridge Marketplace developments.

Vice Chair Robert Klob, a Maricopa resident, called the population projections “a scary number” and said incorporation or annexation could be many years away. Because some of the projects were approved decades ago, he said, developers could theoretically begin construction at any time.

“There’s not much we can do about it. It’s been approved, it is what it is and then we got to clean up the mess afterwards and I don’t like cleaning up messes,” he said.

Klob urged the county to be more proactive and to explore alternatives, though he did not specify what those might be.