G. C. Edmondson was the working name of science fiction author Garry Edmonson (full name "José Mario Garry Ordoñez Edmondson y Cotton") (October 11, 1922 in Washington state – December 14, 1995 in San Diego, California). According to the obituary published in Locus Magazine, Edmondson was born in Washington state During World War II he served as a U. S. Marine.
Although generally called a science fiction writer, he wrote Westerns using the names Kelly P. Gast, J. B. Masterson, and Jack Logan. As he could also speak six languages he did translating work as well. His science fiction career began during 1955 with a story in the magazine Astounding. He later produced several novels which gained some note for their interest in time travel and Latin America. Several writers, including Gardner Dozois, tend to consider him as a neglected author.
The Ship That Sailed the Time Stream (1965) Nebula Award nominee for Best Novel
Chapayeca also published as Blue Face (1972)
The Man Who Corrupted Earth (1980)
To Sail the Century Sea (1981)
Novels written with C. M. Kotlan
The Cunningham Equations (1986)
Stranger Than You Think (1965)
G. C. Edmondson at the Internet Speculative Fiction Database
Biographical information at George C. Willick's SPACEFLIGHT
Works by G. C. Edmondson at Project Gutenberg
Works by or about G. C. Edmondson at the Internet Archive
Works by G. C. Edmondson at LibriVox (public domain audiobooks)