Puerco Pueblo, which is about 11 miles from the north entrance of the Petrified Forest National Park, is the site of one of many solar calendars that have been discovered throughout the Southwest, according to NPS. A short trail leads to a boulder featuring a small spiral petroglyph that marks the summer solstice. For about a 2-week period, a shaft of sunlight is projected onto the boulder and travels down the side to touch the center of the spiral, peaking about 9 a.m.