Born 1966 in Colorado?

Some information I have is from the birth mother's letter of what was going to happen, but I can't say for sure that it happened. Some is heresay... I'm looking for a half sibling, most likely male. Born in the fall of 1966 at Mercy Hospital in Denver, Colorado (mother 18, father 21). The father (mine) was previously married & divorced with 2 boys when he got her pregnant, so the mother's parents would not let her marry my father. I believe they were Catholic. The baby was due in the fall of 1966. My father was in boot camp on his way to Vietnam, so he could not do anything about her giving the baby up for adoption.