Simple process of deduction, Watson.

The two rides are on the same day, as shown on: http://www.marincyclists.com/html/Ma...05MtTamDbl.htm

The 2006 California Triple Crown Schedule states the Mt Tam Double is on 8/5/06: http://www.caltriplecrown.com/schedule.htm

Therefore, the Marin Century is on 8/5/06

The Holstein is a couple of weeks later and, therefore, a different weekend.