So far, only New York, Maryland and Vermont have banned fracking altogether. But none of those states have anything close to the reserves of Colorado, which is among the top six states in both oil and gas production.

Not surprisingly, the initiative has deepened political fissures in a purple state whose economy counts on oil, but whose lifestyle hinges on access to pristine wilderness. As Colorado’s population has climbed, driven by the cost of living, a growing technology sector and the appeal of the outdoors, the state’s new and old industries have collided. At the same time, environmentally-oriented companies like Patagonia are pressing to become bigger political players in the region, often putting them at odds with the oil and gas lobby.

If passed, the measure — Proposition 112 — would require companies to place new wells at least 2,500 feet from homes, schools, waterways and other areas designated as “vulnerable,” two-and-a-half to five times the current state regulation. Even as the measure faces fierce resistance, industry leaders and environmentalists alike acknowledge that it could succeed. One recent industry poll obtained by The New York Times showed 43 percent of voters in favor, with 41 percent opposed.

In recent years, Colorado oil and gas well operations have come so close to homes, schools and playgrounds that drill rigs, holding tanks, diesel trucks and floodlights are now common neighborhood features. In places like Weld County, the center of the state’s boom, residents increasingly fear they are exposing their children to chemicals. A series of deadly industry incidents has only heightened concerns.