A shadow is cast behind an object when the object is between a light source and the shadow it creates. The Sun sets at dusk in the West over The Pacific Ocean. If what you are seeing is a shadow of a contrail you would have to be the Sun as the dark line you refer to appears to the left and therefore behind the plume.
The darker red illumination of the exhaust plume at the horizon is cause by that part of the sky already beginning to be in darkness whereas the upper part of the sky is still lit from the Sun at an angle below the horizon. The proof of this is that the foreground of the photos is already darkness of the terminator.
The Rick Warren photos are clearly no proof of a jet aircraft arcing Easterly over the USA.
The shadow extends to the southeast, which is in front of the contrail. Leftward doesn't translate to westward in this scene.
The darker red illumination of the exhaust plume at the horizon is cause by that part of the sky already beginning to be in darkness whereas the upper part of the sky is still lit from the Sun at an angle below the horizon.
That's not quite right since reduced illumination causes things to become darker, not redder. But you've made me rethink exactly why it is that the base of the contrail is obviously more distant than the upper part. It's not really the redness, which is mainly due to the sunlight at the lower angles having to pass through more lower atmosphere which scatters out more of its blue wavelengths, making it appear redder (the reason sunsets are red).
Instead it's that the base is hazier and less detailed, which is consistent with it being more distant. Also that it's more diffused -- more spread out, in fact a lot more spread out -- which means it was expelled from the plane quite a bit earlier. The only way to account for the extra diffusion time is if it's receding back towards the horizon to the west.
The Rick Warren photos are clearly no proof of a jet aircraft arcing Easterly over the USA.
Yes, actually they are.