The Rim Fire, which by Friday was declared 32 percent contained, has already scorched more than 202,000 acres—destroying Berkeley-owned Tuolumne Family Camp, devouring prime acreage within Yosemite National Park, and menacing other camps and thousands of homes.

And yet, nothing about this fire is anomalous. Large and destructive wildfires ravage the state with metronomic frequency, and for a very good reason: California’s wild lands constitute a fire ecology. Our most iconic native flora—oaks, redwoods, bunch grasses—evolved with fire. Many of our indigenous plants are serotinous, meaning they need fire to release their seeds. In a very real sense, California’s forests and grasslands must burn to thrive.

There’s a difference, of course, between burning and burning up. Drought or near-drought conditions such as what we’re seeing now dry fuels to the point that wildfires manifest as apocalyptic conflagrations, as opposed to the low-level, meandering burns that kill pathogens and insects and return nutrients to the soil. Also most of the computer models tracking climate change indicate fires like the Rim Fire—named for an overlook in the Stanislaus National Forest called the Rim of the World—are going to be increasingly common in the hotter, drier planet our descendants will inherit.

But something else is going on in California, something that is making wildfires far more destructive and dangerous than they were 20—or even 10—years ago: the growth of interface. No, we’re not talking computer science. This is urban interface—the intrusion of luxury homes, condo developments, resorts and shopping complexes into areas formerly vacant save for the trees and critters.

Interface growth inevitably means more property and people are imperiled during fire season. And this, in turn, increases the threat to wildlife fighters. When not burdened by the onus of protecting human lives and homes, wildfire fighters can employ techniques that minimize risk. For example, instead of launching direct assaults to the head of the fire, lines can be dug well away from the main blaze and fuels burned out to the encroaching flames.

But when homes are threatened, firefighters inevitably must switch strategies. Wildfire fighters have to perform more like urban firefighters, using engines and hoses rather than hand tools, and they must directly engage burning structures. They thus face double the risk. They are still subject to all the dangers of wildlife fighting, but at the same time they have to confront the challenges unique to structure fire-fighting.

And sometimes, things go seriously wrong. As New York Times science writer Andrew Revkin noted, the recent immolation of 19 members of an elite U.S. Forest Service “hot shot” crew from Prescott, Arizona, can be largely attributed to the fact that they were engaged in the urban/wildland interface near the town of Yarnell.

And Arizona’s interface growth is modest when compared to California’s. That’s making for an extremely challenging situation in the Golden State. Julie Hutchinson, a battalion chief with Cal Fire, the state agency responsible for fighting wildland blazes, elaborates:

“We’re having to focus on protecting property now, and that has really increased the complexity of our mission,” she says. “The risk to firefighters is greater, and so is the resource demand. On a big fire 20 years ago, maybe we’d have 40 engines committed. Now, it could easily be 240, all because of interface growth.”

There’s an obvious solution here, of course: Control the growth of the urban interface. And the state, continues Hutchinson, is basically behind the idea.

“The State Fire Marshal supports changing development standards in wild land areas,” she said. “The office is working with local jurisdictions to tighten zoning where it’s needed.”

Californians hate it when their houses burn down—but they also hate being told what to do, including where they can or can’t build their dream homes. So how have woodland residents taken to the proposed zoning strictures?

“There has been some resistance,” acknowledged Hutchinson. “This is a collaborative process. People have rights when it comes to the development of their property. But public safety is also an issue. The development has to be appropriate to the risk.”

—Glen Martin

For updated information about the fire itself, see California Magazine’s blog coverage of Rim Fire.