You can find seashells along most sandy stretches of the Oregon Coast. I feel timing and technique are the more critical aspects to beachcombing for shells rather than a specific location. For best success, I would suggest choosing less busy beaches, beachcombing during the offseason and being there at the right time (as the tide recedes). I like to beachcomb for shells right at the edge of receding tide, weaving in and out with the waves, always keeping my eyes on the tide and being prepared to move quickly in the event of a sneaker or rogue wave that may come in faster and higher than the average waves.
For shells, I would begin searching an hour or two after high tide since most heavier shells aren’t deposited on the beach until closer to the low tide line (but you want to be the first to discover the freshly revealed prize). As you scour the beach, look for deposits made up of ground bits of seashells. Look close at these deposit because common finds include sand dollars and scallops that can be smaller than a dime. You can also look in areas of small rocky deposits where snail shells can be mixed in.
The variety of shells may vary with the surrounding environments. You are more likely to find snail shells and cone shaped limpets near rocky shores or off shore reefs, clam shells near bay openings and sand dollars and scallop shells along beaches that border shorelines with sandy offshore bottoms.