PITTSBURG -- The conservation group Save Mount Diablo has alleged that the developer Albert D. Seeno Construction Co. may be illegally grading hillsides along the Los Medanos ridgeline in Pittsburg for its San Marco housing development.

Save Mount Diablo has sent letters and aerial photographs to Pittsburg and Concord city officials calling for an investigation into the developer's alleged grading activities.

The letters accuse the developer of destroying a seasonal creek and related tributaries and marring the view along the ridgeline on both the Concord and Pittsburg sides of the Los Medanos ridgeline, possibly violating the Pittsburg General Plan and an agreement with Concord not to allow Pittsburg development to be visible from Concord.

"The creek is gone -- they simply graded it out of existence," Ron Brown, executive director of Save Mount Diablo, said. "The creek once started at the ridge and ran all the way to Highway 4 in Pittsburg. They bulldozed the stream all the way up to one of the area's highest knolls."

The group has also reported that the grading is already showing signs of erosion and could impact soil stability and increase landslides in the area, particularly given the steepness of the hillside. Conservationists are also concerned about potential impacts on endangered species habitat.

Representatives from Seeno Construction Co. did not return phone calls Monday.

"We are already aware of this grading and are having the situation reviewed by our Engineering Department. Thank you for providing us with your input," Pittsburg City Manager Marc Grisham wrote Friday in an email response to Seth Adams, director of land programs for Save Mount Diablo.

Adams said that the California Department of Fish and Game had begun an independent investigation into the developer's grading projects.

According to Save Mount Diablo, Seeno has had several major violations in the past. In January, the developer was fined more than $3 million for illegal grading at its Mira Vista subdivision that destroyed ponds and several creeks in Antioch.

In July 2002, Seeno's West Coast Home Builders paid $1 million in fines and restitution after pleading guilty to violating the federal Endangered Species Act for its 2001 killing of threatened red-legged frogs and deliberate destruction of frog habitat at the San Marco development in Pittsburg, part of the same development project currently in dispute, according to Save Mount Diablo.

In 1989, Seeno was reportedly caught removing heritage-sized oak trees at its Crystal Ranch project in Concord before the environmental impact report had been prepared, Save Mount Diablo reported.