To facilitate administration for the purpose for which the preserve has been established, the western boundary of the preserve lying north of Custer State Park is redefined as follows:
Beginning at the east quarter corner of section 7, township 2 south, range 5 east, Black Hills meridian; thence south along said section line to its intersection with a line three hundred feet north of the Horse Thief Lake Road; thence southwesterly along a line three hundred feet northwesterly from the center line of said road and running approximately parallel thereto to the intersection of said road with United States Highway 85A; thence southerly along a line three hundred feet west of United States Highway 85A and approximately parallel thereto to the present south boundary of said preserve in section 3 south, range 4 east, Black Hills meridian.