(Portland, OR)  --  An investigation is under way into the theft of a van filled with irreplaceable Native American artifacts and heirlooms in southeast Portland.  Wolf and Lisa Wahpepah of California tell KATU they were in Portland for a recent inter-tribal sun dance ceremony when someone stole their van from the parking lot of the Nielson Mobile City mobile home park Saturday night.  The couple says they had just loaded everything back up into their trailer and were preparing for the journey home when the theft happened.  The couple is now stranded in Portland, because the van was their only means of transportation.  The stolen artifacts include things like pipes, eagle feathers, bone whistles and ribbon dresses.