Marine Base Expansion Will Limit OHV Recreation

The Twentynine Palms Marine Base released a draft Environmental Impact Statement (draft EIS) for its proposed expansion, which would put over 146,000 acres of the Johnson Valley Off-Highway Vehicle (OHV) area under military control for live-fire exercises.  The military has reportedly met with OHV groups to work out arrangements that give OHV users access to part of the exercise area when it is not being used by the military.  As a result, the Marines' preferred alternative would let OHV users access a portion of the area during 10 months out of the year.

The Johnson OHV area is one of the largest in the Mojave Desert, and draws thousands of OHV enthusiasts each year.  OHV use takes a heavy toll on the viability of desert habitat, so much of the area has already been degraded by years of intense OHV use.  However, desert plant and wildlife would still be impacted by the heavy military use of the area, and the Marines expect that anywhere from 121 to 189 adult desert tortoises could be impacted in the acquired training lands, although more would be impacted by translocation and testing activities.  The military would attempt to mitigate impacts on the crucifixion thorn, a special status plant species that grows in rocky desert washes.

The map above shows the expansion of the Twentynine Palms base westward into the Johnson Valley OHV area.  The red shaded areas would be permanently restricted, but the yellow shaded areas to the south would provide for public access during certain times of the year.

The military assesses that biological resources could benefit overall in areas restricted to public access because the reduced OHV usage would decrease harm to biological resources.  The military would designate specific areas for exercises, but other areas would be left relatively untouched.  In its survey of the biological resources in the Johnson OHV area, many "highly disturbed" lands were identified as a result of the constant OHV recreation use, including the area photographed below.

The photo below was included in the Marines' biological resources survey as an example of the highly disturbed land in the Johnson OHV area.  The assessment notes that multiple vehicle tracks, RV staging areas, and hill climbs resulted in vegetation loss that severely degrades the quality of the desert habitat.  Once transferred to military control, the report assesses that overall negative impacts on the land would be less than if it were to remain as an OHV recreation area.

However, some of the proposed military exercise routes would still impact areas that could have relatively higher desert tortoise density.  The exercise routes are not yet final, and should be adjusted to avoid the most biologically intact habitat.  Some of the areas under consideration for high impact exercises are assessed to host tortoise densities up to 31 tortoises per square mile. Not surprisingly, most of the most biologically intact areas appear to be in parts of the OHV area that are less accessible or contain fewer vehicle race course routes.

The western portion of the map assesses desert tortoise density per square kilometer, with an overlay of theoretical exercise routes that would have high impacts.