On the beach were teepees made of three sticks standing up. This specific teepee had a rock on one of the sticks. I focussed on the rock and the stripes on it. I believe that these stripes came from the years the rock was laying in the sand and water. When the sand-water flowed around the rock, it created these stripes. In addition to the stripes on the rock, the waves created subtle stripes in the background.