Portland Memorial Mausoleum/Oaks Bottom Wildlife Refuge Half Completed. Soon to be the largest mural in the U. S., a wetland motif is being applied to 50,000 square feet of west and south facing walls of the Portland Memorial Mausoleum, which overlooks the 160-acre Oaks Bottom Wildlife Refuge. The mural is so large it can be clearly seen from I-5 on the west side of the Willamette River.