Dude, you were out at the low tide and you still couldn't get what you were hoping for? Were they not squirting into the air? Steamer shows aren't always apparent, especially if the area you are in has a mix of shells, sand, mud, gravel. I would say that best success is digging in areas where the beach is gravelly... same place you'd fish for cutthroat. They are shallow so if you find yourself digging past two shovel blade lengths, you're probably too deep.

Another tip: always pay attention to the sea gulls... if one starts sticking his nose in the ground, keep tabs on him... when he gets a clam, watch the bird wrestle the clam out of the beach and then see the gull fly away to higher ground and drop the clam on the rocks in an attempt to crack the clam open. Then it's your duty to liberate that clam!!! :p

On a side note, got to watch a sea gull win a tug of war with a horse clam today. A while later I checked back on the clam and the sea gull had cleaned out all the meat