Native American pottery shards

My parents are still moving into their downtown apartment — right next to the one we’re presently occupying — and last night, amidst a drawerful of seemingly unrelated objects, I noticed the vintage Tang jar in the photo below.

The jar is full of pottery shards my dad picked up near a rest area round about 1966. He was traveling with friends in the Pueblo, Colorado area.

Pieces range from about 3/16 to 3/8 of an inch in thickness. The black and red shards are very smooth, probably terra sigged and burnished to a shine while the lighter colored ones with decoration bear a quite dry surface.