Environmentalists say the land near many Gold Rush-era mines is contaminated with asbestos, arsenic and lead…and exposure to these toxins is increasing.

"As the population of California grows, more people are moving into these areas. And then you have people who are recreating and working throughout the Sierra."

Mike Thornton is with The Sierra Fund, the environmental group hosting the conference titled "Reclaiming the Sierra". He also says many sierra rivers have high levels of mercury because of hydraulic mining done 150 years ago. Thornton says cleaning up the sierra is not only good for the environment…it would also create jobs…

"…whether it's assessment, whether it's actual cleanup of the mercury or the old mine sites, that needs to be done sooner or later."

The two-day conference ends tomorrow.