[2] CR 66 begins at its western terminus, on the National Trails Highway at the intersection of 1st Street in unincorporated Oro Grande, near the Victorville city limits.

After an overlap with Interstate 15 Business (I-15 BL), it continues south to the I-40 interchange, where it runs concurrently with I-40 east for four miles (6.4 km) before splitting from the freeway at the Nebo Street exit.

[1] At 175.7 miles (282.8 km) in length, CR 66 is the longest county route in California,[citation needed] and it is even longer than some Interstate highways.

[3][4] The CR 66 sign program began in San Bernardino County in June 2011,[5] defining the route from just north of I-15 in Victorville to US 95 northwest of Needles.

[11] San Bernardino County Public Works is in the process of replacing 128 timber bridges in excess of 80 years of age.