The Mustang Mystique: Descended from animals that escaped the Spanish conquistadors almost 500 years ago, wild horses roam the West. But are they running out of room?

To create her haunting, intimate photographs of wild mustangs, Melissa Farlow staked out water holes across the West. In Nevada's Jackson Mountains, she slathered on sunscreen; in Oregon's Ochoco National Forest, she wore snowshoes. Visiting a South Dakota mustang preserve on a Sioux Indian reservation, she was lost in fog for what seemed like hours; at last she heard a soft nicker from a horse just 20 feet away, hidden in the mist.

When Farlow was photographing a herd in Oregon's remote Steens Mountain area, a pinto stallion charged out of the sagebrush at her, hooves churning. "All of a sudden I just sat down," Farlow said.

It worked. Seemingly assured of his own supremacy, the stallion quit snorting and stomping, and before long the photographer found herself being sniffed by mares and foals.

Farlow spent part of her childhood astride a …