The five foot deep foundation holes are built up with large material to make peers below grade. Side planks make temporary bridges to transport building material over the creek
Each layer of carefully fitted foundation stones is hearted with stone chips and gravel around the joints, being careful not to have stones wedging gravel between of the stones above and below. That would make the gravel susceptible to acting like marbles and causing the stones to roll sideways.
A crib of cedar posts is made in the creek to support the form
It looks like a mess, but it's a very controlled mess.