[D-fendr]

In that case why doesn't the contrail continue on and cross overhead and then continue on to the east?

It leaves the contrail-persisting region of air. Here's a contrail calculator that gives the variables involved in whether contrails form or not:

Contrail Critical Temperature Calculator and Contrail Diagnosis

[TigersEye]

Yes, I’m well aware that not all air conditions propagate contrails. The air conditions over the entire region from LA to Phoenix yesterday were cold enough and humid enough to create them the entire flight path. We just had a front move in to CO last night that extends at least as far south as the Mexican border.