Clamming is legal through July 15. Oregon requires no clamming license, so clam to your heart's desire in low tide, in any clam-rich areas like Garibaldi, Rockaway, Tillamook, or Nehalem Bay (all a little over an hour north). Another good spot is south, just east of Florence in the estuary area north and south of the North Fork Bridge on Hwy 126 (dune-filled Florence is also a great vacation spot--about 3.5 hours).
Search out a spot where the water has retreated, but the sand is still wet. Look for small holes in the surface. Your clamming fork is shaped like an "L". Jam your fork into the mud next to the hole and lever it up. hopefully with a bunch of clams on it. If they wiggle away, keep digging; clams are smarter than they look. Throw your clams in a bucket and fill it with seawater so the clams flush out the mud. Later, clean them with fresh water. To cook the little buggers, put a splash of white wine and a big pat of butter in a skillet. Boil them alive at medium heat for about five minutes (they'll be dead and tasty by then).
Warning: Be sure to call the Oregon Agriculture Department at 503-986-4720 to check the domoic acid levels. Clams filter the water around them and get their revenge by poisoning you.