You have an instrument rating and fly in Colorado and don't know what an obstacle departure procedure is?
The primary purpose of most DPs is traffic flow or shortening reading clearances, like the DENVER THREE SID. An obstacle DP is a DP that has a different primary purpose: keep you from crashing into terrain.
Open your IAP book and take a look at the GYPSUM THREE (OBSTACLE) DP for Eagle airport.
It's also here:
http://www.naco.faa.gov/d-tpp/0410/06403GYPSUM.PDF