Planning for development at Donner Summit should protect existing community values and address water supply, wastewater treatment, road congestion and fire safety, regional conservation groups said in a letter delivered Thursday to Nevada and Placer county supervisors.

Development also should protect the summit's natural and cultural resources, environmentalists argue in the letter, signed by nine Sierra conservation groups to increase pressure on a development project proposed for the summit.

The letter comes as owners of the Royal Gorge Cross Country Ski Resort prepare to unveil their own development plans.

"This is going to be a long-term effort," said Tom Mooers, executive director of Sierra Watch, the group that spearheaded the letter campaign.

In 2007, Sierra Watch and Sierra Club enlisted planners, biologists and hydrologists to assess how the Royal Gorge development would impact resources in the region. Findings from the survey undergird the letter's blueprint.

Developers Kirk Syme and Todd Foster call their development a conservation community, with 950 housing units in four clusters with outdoor recreation, skiing and open space.

"The region is the most important cultural crossroads of the American West, with a rich history written in the rock art of the Martis Indians, the wheel ruts of the first wagon trains and the snowsheds of the transcontinental railway," the letter reads.

Groups signing the letter include the South Yuba River Citizens League, Red Bud Chapter of the California Native Plant Society and the Sierra Foothills Audubon Society.