A 21st-century development surge has transformed at least 525 square miles of Colorado, an area bigger than Rocky Mountain National Park, as once-wild land vanishes across the West.

The urban expansion, road-building and energy production is causing a breakup of natural space that threatens wildlife as people push into their habitat.

A bear walking a random path couldn’t go farther than 3½ miles on average before encountering “significant human development,” according to an analysis by Conservation Science Partners, being unveiled Tuesday at the Center for American Progress, a Washington, D.C., conservation group.

Colorado ranked second to California (785 square miles) in total natural area affected. Development across 11 Western states now covers more than 165,000 square miles, with more than 4,321 square miles converted since 2001, the “Disappearing West” study found.

And urban sprawl, commerce and drilling claim the equivalent of a football field every 2½ minutes — roughly a Los Angeles-sized area of open land per year.

Interior Secretary Sally Jewell has cited the study, calling for a renewed emphasis on large-scale planning. Jewell warned against “a haphazard web of transmission lines, pipelines and roads” and that “if we stay on this trajectory … national parks and wildlife refuges will be like postage stamps of nature on a map — isolated islands of conservation” that people visit like zoos to try to glimpse nature.

Saving open space would require “big-picture, roll-up-your-sleeves, get-input-from-all-stakeholders” planning, Jewell said, and cannot be done by simply creating new parks.

“We’re losing a lot. We’re losing the natural lands that Westerners and other folks appreciate,” said David Theobald, a Colorado State University geographer and conservation biologist and the Conservation Science Partners senior scientist who led the study.

The transformation in Colorado is happening at rates “comparable” to the Front Range suburban boom of the 1970s but with new human activities playing a greater role, Theobald said.

“If we want to have wildlife populations be able to move across the land, the most widely recommended strategy is to maintain connectivity of landscapes,” he said. “If we are increasingly fragmented, that does not bode well.”

The researchers analyzed a decade of satellite imagery and 36 sets of data covering public and private lands in each of the states (Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington and Wyoming). They defined “natural areas” as land with minimal human influence — a spectrum ranging from open parcels in cities to wilderness.

Roughly three-quarters of the land transformed from 2001 through 2011 was privately owned. The bulk of the natural land converted was outside cities — areas such as Weld County north of metro Denver.

Main driver: energy development, which drove 32.7 percent of the transformation in Colorado.

“Urban sprawl” expansion caused 22.3 percent of the change in Colorado. Transportation activities drove 4.1 percent of the total land transformed.

Agriculture and tree-cutting activities, which in the past covered 13,000 square miles, played relatively minor roles this past decade.

The researchers were in the process of updating their Disappearing West data to this year with an emphasis on determining rates of change. They’re trying to help state, county and city officials — along with land trusts and other nonprofits — invigorate landscape planning.

Since 1962, Colorado leaders have raised concerns about development devouring open space and wrestled with implications of growth control. Gov. John Love oversaw a study using maps to consider scenarios for the future along the Front Range.

“Today we have better technology and information to describe what is happening,” Theobald said.

“But do we have a will, as a society, to face these tough issues? Fifty years later, they’re still there.”