Generally there are gas stations and 7-11's along the way.
I did the Santa Fe Century when I was 59, and I didn't start "riding" until I was 58.
Of course you are exhausted at the end - that is sort of the point!
And your goal is NOT x miles per hour. Your goal is to finish, as plain as that.
Please see:
http://members.aol.com/dnvrfox/santafec.htm
for pictures and a description.
Here is a sample.
Or, if you want to come to Denver, I can take you on 100 miles of trails in a circular loop, with all the support you need from stores along the way.