MEAD, Colo. (AP) — Workers bustle at an oil and gas drilling site near Mead, Colo., a town of about 3,800 people north of Denver.

The hydraulic fracturing operation, also known as "fracking," and others like it pump hundreds of thousands of gallons of water, mixed with fine sand and chemicals, deep underground to split the rock, and make the oil — and dollars — flow.

But the drilling has come much too fast — and too close — for several communities, where fracking bans have been enacted out of concern about its possible impact on groundwater. The state government and the energy industry are challenging those prohibitions.

In this photo essay, AP Photographer Brennan Linsley looks inside a walled-off fracking facility, one of many sites reversing decades of declining oil production in the state.