The only long distance service from Denver is run by Amtrak. The only train that actually stops at Denver is the California Zephyr (Chicago, IL - Emeryville, CA), with one train in either direction per day. Other connections can only be made by chartered busses. The small number of trains on Amtrak's western long distance routes makes train to train transfers difficult. The first leg of my journey to Los Angeles is actually not by train but by a bus to Raton, New Mexico, where I will catch the Southwest Chief at it's 10:50AM stop there.