Signed Original Ansel Adams Photograph - what is it worth?

This is a signed 7 x 9 inch photograph by Ansel Adams titled El Capitan, Winter. I was told that he developed it himself and its matting is signed with his signature. It says on the back the title, and that it's number 104 of S.E.Y. number 17. I mainly want to know its value so I know what to insure if for. My parents gave it to me as a Christmas gift, and have two more (one of their's has a tiny tear at one corner). All three were found on top of a closet in my grandmother's house, unframed but matted and signed. Maybe a gift to my cardiologist grandfather from a wealthy patient way back when?

Excellent