I wasn't in SF for too long, but I of course had to make the requisite trip to Mo's.
alpine burger - sauteed mushrooms and gruyere - $7.75
Excellent as usual. This is truly one of the places you must hit if you go to San Francisco. I really have yet to have a burger anywhere that can beat Mo's. They grind their own meat and grill it perfectly. When you order it medium rare it actually comes bloody. And, to my complete surprise, the prices have actually gone down since the last time I went. The alpine burger used to be over $8. I also highly recommend the belly buster burger.
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