The letter featuring the agency's logo was apparently sent to area residents and circulated online. The letter claims "California is issuing a statewide warning" and five communities -- Westminster, Santa Ana, Long Beach, Newport Beach and La Habra -- could experience a 7.4 magnitude "tremor."
Instead, the agency advised residents to check the USGS website for the latest earthquake information.
The letter comes after Friday's 5.1 magnitude temblor centered in La Habra. The quake was felt across a large swath of Southern California. It caused modest damage to some homes, a rock slide in Carbon Canyon and broke some water mains.
An estimated 17 million people felt the quake, according to the USGS Did You Feel It? online reporting system.
Since then, the region has continued to experience aftershocks, most recently Tuesday, when a 2.8-quake struck near La Habra at 6:02 a.m., according to the USGS.
[For the Record 10:55 a.m. PDT April 1: An earlier version of this post incorrectly referred to the U.S. Geological Survey as the U.S. Geological Society.]