LAS VEGAS (AP) — Plans to expand a mountain resort outside Las Vegas to offer recreation opportunities during summer months have sparked a lawsuit from conservationists worried about the effects on a rare butterfly and its habitat.

The Center for Biological Diversity filed a federal lawsuit on Nov. 19 to block the expansion of the Lee Canyon Ski Area, a ski resort in the Spring Mountains about 25 miles (40 kilometers) from Las Vegas, claiming proposed mountain biking trails and other development proposals could threaten the area's endangered Mount Charleston blue butterfly.

The butterflies are less than an inch long and live at high elevations. The U.S. Department of Fish and Wildlife listed the species as endangered in 2013, setting the stage for struggles with developers hoping to expand the resort to keep pace with population growth and demand in southern Nevada.

Powdr Corp., the resort's owner, is seeking approval to add mountain biking trails, zip lines and a roller coaster to its current offerings, the Las Vegas Review-Journal reported. Some of the proposed infrastructure lies on land that belongs to the U.S. Forest Service.

Conservationists have long argued that the development will threaten the tree canopy openings the butterflies flutter between in their habitat.

In the lawsuit, they challenge a June biological assessment and October Environmental Impact Statement from the U.S. Fish and Wildlife Service and U.S. Forest Service, respectively. Both are cited in the Nov. 9 U.S. Forest Service draft decision that approves a proposal in the Lee Canyon Ski Area Master Development Plan.

"It's outrageous that the government would allow the most important remaining habitat for this beautiful little butterfly to be turned into a downhill-sports amusement park," said Patrick Donnelly, the center's Nevada director. "The Mount Charleston blue butterfly hangs by a thread, and we don't intend to sit idly by while the Forest Service lets a multinational corporation destroy what remains of the species."

Lee Canyon General Manager Dan Hooper believes the expansion is an example of responsible growth, the Reno Gazette-Journal reported.

"A part of Lee Canyon's core values and Play Forever commitment is to be stewards of the mountain and to ensure our community that when they recreate at Lee Canyon, they're doing so responsibly," he said. "The authorization of improvements at Lee Canyon is a win for local outdoor recreation and the environment."

The butterfly, which lives less than a month and is a luminous blue-gray color, has been threatened in recent years by wildfires, invasive species and climate change.