These are Eroded Periwinkles (Littorina keenae) in a narrow crevice in the splash zone (the highest level of the rocky intertidal zone). They live higher than any other marine gastropod. They can be out of the water for such long periods of time that some people might consider them semi-terrestrial.
They're called Eroded Periwinkles because their shell erodes as they age.
This is a helpful characteristic when you're trying to identify them, but if you only look at larger, older individuals, you miss out on the wonderful variation and patterning of the juveniles:
As you can see, some are pale, others are dark (mahogany brown?), and they have variable amounts of white. It's amazing how well these combinations match the surrounding rocks.
Below are two more examples of the pale and dark forms:
Although they blend in well, once you know what to look for, I'm guessing you'll find some Eroded Periwinkles in splash zone crevices during your visits to the coast.