Retamoza completed her first Duramed Futures Tour victory at five-under-par 208, one stroke ahead of last year's winner, Ha Na Chae, who closed with her second straight 69 to post minus-four.
Retamoza, a native of Mexico, climbed to sixth on the money list with the $11,200 first-place check.
Brandi Jackson also shot 69 to end alone in third at three-under-par 210.
Cortney Reno, who led entering the final round, struggled to a two-over 73 to finish tied for fourth at minus-two. She was joined there by Alissa Kuczka, Kelly Cavanaugh and Kim Welch.
Liz Janangelo, a two-time winner this year, shot 69 to finish alongside Sofie Andersson and last week's runner-up, Mollie Fankhauser, at one-under-par 212.