I have been in similar traffic....
one time on June 2009 on my way from LA to Las Vegas....
There was a horrible car accident on the I-5 that I recalled speding 3 hours in traffic. Traffic was stopped completly that everybody turned off their cars and got outside at the 115 degree temperatures and started playing soccer, taking pictures, sitting down in the freeway...
I would say traffic was backed up for a good 15-20 miles.