beach cliff strata

My wife and I were walking on the beach, and we saw this:


We were wondering what made the white layer in the cliff face. I'm pretty sure it was laid down as the top soil at some point in the distant past, but why is it so white, and is it the result of ones years deposit, or multiple years. Obviously the white is a different material from the other layers, but what was happening at that time that made the material being deposited on the surface so different.

For context this is a cliff near the beach south of San Francisco.

If someone knowledgeable could give some guesses as to the answers to these questions, I would appreciate a response.

Thanks.