The Hat Creek Radio Observatory (HCRO) is operated by the SETI Institute in the Western United States.

Hat Creek Radio Observatory is located approximately 467 km (290 mi) northeast of San Francisco, California at an elevation of 986 m (3235 ft) above Sea Level in Hat Creek, California (in Shasta County).

Latitude: 40° 49' 03" N; longitude: 121° 28' 24" W. The nearest large city to Hat Creek is Redding, California on highway I-5.

[1] The SETI Institute started a refurbishment and upgrade program for the ATA in 2019, and in 2020 it also took over the operation of the observatory from SRI.

The earliest experiments in millimeter-wave astronomy were performed at this site starting in the 1970s when a 2-element interferometer was constructed.