Post this on the OGR (antique roses) forum, and I'll bet you get a knowledgable answer from Mendocino Rose. Looks like Darlow's Enigma to me.

Kathy

Wrong bud color and inflorescence too dense.

Wow that's a beautiful rose.... I'd take a cutting from that one and try to start a new bush for yourself....

I don't know if you got an answer on Antique Roses forum, but it might help to contact the Mendocino Botanical Gardens and see if someone there knows its identity:

http://www.gardenbythesea.org/index.cfm/fuseaction/home.contact/index.htm

Sally Holmes maybe?

That one produces large single (or nearly single) flowers.

Maybe Trier?

I thought of that one also. Does it produce pink buds?

The blooms look similar to pictures I've seen of a rambler called Thalia.