No this has nothing to done with some foul, slimy creature crawling out of a lagoon. There are a lot of localized place names that over the years have been forgotten and abandoned. One example is Murphy field, where Bob Murphy and Finn Barry after graduating from college tried their hand at farming in 1916. It did not take long for Finn to give up the farm and went on to become an attorney.
Swamp Angel is located in the Tule District, near present day Fleming Unit of the California Department of Fish & Game, and Murphy field nearby. Its name arose during the Civil War. The region was known as the Tule Confederacy, due to the concentration of Southern sympathizers who resided there. There were several conflicts in the region between those of the Union and others supporting the Confederates. The Swamp Angel was the name of a Parrott siege gun used during the preparation of the bombardment of Charleston, South Carolina in August 1863.