[medved]

That's an awful lot of sandstone, wouldn't you agree? Also, wouldn't you agree that with that much sandstone, a massive electrical discharge just might leave some traces of fulgarites?...

Not if the electrical discharge in question is the wrong kind (anode vs cathode scarring). The other thing I could mention is that lightning strikes which leave fulgarites are on a much smaller scale than the thing I am describing and that could easily have something to do with it.

[VadeRetro]

The other thing I could mention is that lightning strikes which leave fulgarites are on a much smaller scale than the thing I am describing and that could easily have something to do with it.

It blasted this big trench in the sediments but didn't heat anything up enough to fuse sand to glass?

[VadeRetro]

Where's the rubble of this eruption? The debris field? Sure, stuff washed away downstream, but all that stuff thrown to the side should be there, right?

[Scully]

Not if the electrical discharge in question is the wrong kind (anode vs cathode scarring).

I'm not an electrical engineer (maybe some kind-hearted soul out there will help), but in the event you are describing the electrical discharge would have to travel from the space body to the Colorado Plateau to cause surrounding terrain to vaporize. Since electricity by convention travels from positive to negative, this necessarily means the earth would act as the cathode...not the other way around.