COMMISSION

Clear Creek Management Area
The Clear Creek Management Area (CCMA) consists of approximately 75,000 acres of
mostly public land within the southern Diablo Mountains of Central California. It extends
from southeastern San Benito County into western Fresno County. BLM manages
63,000 acres of the public land within CCMA.
The CCMA has been recognized as one of the top motorcycle trail riding areas in the
nation. Hiking, mountain biking, rock-hounding, hunting, and camping are also popular
activities at CCMA. In years past, CCMA received approximately 35,000 visitors annually.
In 1984, the BLM designated 31,000 acres of CCMA as the Serpentine Area of Critical
Environmental Concern (ACEC). This was based on the mapping of soils derived from
the New Idria Serpentinite geologic inclusion and on perceived health concerns related
to naturally occurring asbestos (NOA).
Serpentinite may or may not contain
asbestos—the terms are not synonymous.
The name serpentinite is used because the
metamorphic rock is mostly composed of the
serpentine group of minerals—a collection of
about 20 minerals with similar chemistry but
varying micro-crystalline structures. Most of
these minerals have a platy structure, which
makes the rock feel smooth and waxy. A few
of the minerals, such as chrysotile, appear
fibrous because their internal structure is elongated and flexible. The fibrous serpentine
minerals often appear as veins within serpentinite rock. This small subset of minerals is
generically called asbestiform or asbestos. That said, the New Idria Serpentinite contains
NOA, particularly in the eastern third of the ACEC, where the rock has been mined for the
chrysotile it contains.
After the 1984 delineation of the ACEC, BLM produced maps with NOA information and
posted signs regarding NOA exposure risk, which included recommendations for minimizing
risk, such as avoiding the area during the hottest and driest months of the year. From 2006
to 2008, the BLM managed CCMA using a seasonal closure that extended from June
through mid-October as a means to mitigate NOA risk to CCMA visitors.
In May 2008, BLM issued a temporary closure of CCMA. The closure was in response to
a May 2008 health risk assessment study by Region 9 of the United States Environmental
Protection Agency (EPA) (Region 9) which stated that exposure to NOA at CCMA was “of
concern.” The Region 9 study examined NOA exposure for various recreational activities
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California State Parks, Off-Highway Motor Vehicle Recreation Commission