The one in Protrero Hill, on each side (NW and SE) seems to indicate there was, or is, a tunnel under the hill. Is that so?<p>Edit: Found the answer myself. <a href="http:&#x2F;&#x2F;foundsf.org&#x2F;index.php?title=Potrero_Commons_18th-Wisconson" rel="nofollow">http:&#x2F;&#x2F;foundsf.org&#x2F;index.php?title=Potrero_Commons_18th-Wisc...</a>