The west side of San Marcos is indeed an open roadstead, but gives enough protection from the areas it needs to in order to provide a restful stop for those in transit. The point north of the anchorage provides a bit of extra protection, as well as good fishing and snorkeling grounds. Note that if the wind is light, this spot can get wicked hot on a summer afternoon.
Keep well clear of Punta Piedra Blanca to the north. Otherwise, wide open from any reasonable angle.
The anchorage is much larger than it would appear on the chart, with a sandy shelf near shore that extends well south at least 3/4 of a mile. Anchor in 20-30 feet in good sand with some shell.
Beautiful rocky slopes with cut arroyos that funnel easterly breezes down into the bay. A few nice pocket beaches.
Take the dinghy north to the rocky points and bays around Los Arcos, and check out the sea caves and good snorkeling up there. Great photo opportunities for you and the crew.