I was in the USMC and we were on a bus from Camp Pendleton, CA to 29 Palms, CA. It was the weekend before Thanksgiving. It's normally a 2.5 hour drive or so......it took us 14 hours.
When I was actually driving the worst would be coming into CA from CO. There's a checkpoint on I-15 south of Barstow. I think the traffic jam (I mean actual stop-and-go traffic, not just driving slow) was something like 32 miles. Oddly enough, this was directly following Thanksgiving.
Cliffs: Thanksgiving = bad time to drive