Huge larva found in dead cottonwood.

This larva is 2 inches (50 mm) long.  This beetle larvae was collected from dead wood from a pile of cottonwood.

When Kathy brought this to the office she stated several large dying branches were removed from the top of their tree. This longhorned beetle may have been the cause of the death of those branches. When friends collected firewood from the pile this creature was feeding in the dead wood.

This is the larvae stage of a beetle, most likely a longhorned beetle, Order Coleoptera, Family Cerambycidae, genus Saperba. 

The head end.

We won't really know what species it is until it pupates and emerges as an adult.  That might take some time.