Unless I am missing something, seems pretty clear that the start is at the Colo Welcome/Visitor's center just west of I-25 on Prospect. Depending on where you are coming from, you can join one of the "groups" on their journey to the starting point above. For example, people in Denver are going to meet at 120th and I-25 at 8:15-8:30 then drive up to the Welcome Center for full group departure at 9:30.
08 E90 | Jet Black / Black | 6MT
Mods: RAC RG63 w/ Pirelli Corsa 255F/285R | Akrapovic Evo Exhaust | OEM Blacklines
Winter Setup: OEM 18s w/ Nokian Hakkapeliita R 245/40-18