It a tiny photo so hard for me to see since my glasses broke. But it
looks like blistering. Which is harmless it’s caused from excess moisture and in fact if you’re in San Francisco, for San Francisco sourdough that is coveted.
if you want to get rid of it just make sure that you are allowing for proper absorption of the water into the dough during mixing and before you divide and shape.
make sure there is not too much moisture in your proofing set up.
and when you bake if you’re adding moisture in your oven, make sure you’re not adding moisture directly onto the crust.