Is the XC one lap or more?
XC should be one lap for beginners, two laps for sport, 3 laps for expert, etc. Earlier this season, our local sport riders were finishing the course around 1:30, experts around 2:00. But our local riders are faster than most

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More importantly...is the marathon course (25 miles 8800') one lap or two? Anyone got info on that?
Here's the map. It is one loop.
http://www.teambigbear.com/pdfs/DeerValley_Course_MA.pdf
That is a culmination of some of the funnest singletrack in Deer Valley. Sounds like a great course. I would recommend an XC FS bike for this course. The downhill will be pretty long and rough in spots. Especially at the top of Spin Cycle.
From the map I can't tell what downhill is from Bald Mountain. It appears to be Aspen Slalom from comparison with another map. If it is, then definitely use a light FS. You will be descending lift accessed trails, so they may be a bit torn up. You may want good knobs as well, like a Nevegal 2.1 on front and a lighter faster roller on the rear. You'll be descending 2000 feet all in one shot.