Why the Solar Eclipse shadow moves from West to East

The sun causes a shadow for every object it passes over as it moves across the sky above the flat plane of the earth from dawn until dusk, east to west.

Therefore, at dawn the shadows of a tree or a lamppost are on the west side of the object.
Then the shadow is directly below the tree or lamppost at noon, as the sun passes directly overhead.
Finally, the shadows are to the east of the tree or lamppost, as the sun sets in the west.

It is this exact same movement of the sun which explains why the shadow of the moon moves from west to east.

The sun is at a higher altitude than the moon.

When the eclipse begins, the sun is "rising" above the moon from the east, making the shadow of the moon hit the ground to the west in, say, Oregon. As the sun passes directly above the moon at its zenith ("noon") point, then the shadow will be directly under the moon, hitting the ground in say, Kansas City. Last, the shadow will be to the east of the moon as the sun "sets" to the west of it, causing the shadow to hit the ground in say, Georgia.

The shadow will also be elongated at "rise" and "set," explaining the overall elliptical shape, and more circular at zenith. You can do this experiment for yourself by observing a timelapse photo of the shadow of a lamppost from rise to set.

Here's a good example video: the shadows of these vertical doorposts move across the floor from west to east (left to right) as you see the sun rise in the east (right) side of the camera frame. This shows the exact effect of what happens during the solar eclipse:



It is a much simpler explanation when you know the earth is a flat plane, than the unintelligible one the media/NASA tries to give:

Also, the eclipse shadow is reported to be 70-100 miles wide, so this would be the width of the moon.

The shadow of any given object corresponds to its size. The width of a shadow of an object does not change, only the length, as it elongates due to the lengthening distance of the source light (the sun) and the angle approaching zero.