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The Picture Rocks Sun Dagger is a spiral petroglyph on a hillside northwestof Tucson that shows sun dagger events at both the summer solstice and theequinoxes. On each of these dates, a wedge-shaped sunbeam with opening angles20{\deg}-30{\deg} touches the center of the spiral, with both of these beingconfidently intentionally constructed by peoples of the Hohokam culture c.800--1300 AD. More generally for claimed sun daggers throughout the AmericanSouthwest, the critical question is whether the ancient indigenous peoplesintentionally placed the petroglyph so as to create a solar marker. Theconfident starting point for proving the intentionality of sun daggers ingeneral is a histogram measured by the Prestons showing highly significantpeaks for indicated declinations within 2{\deg} of -23.4{\deg}, 0.0{\deg}, and+23.4{\deg}, with this being not by chance. In a review of solsticial andequinoctal sun daggers, we find that they all have beams of light shaped like along-thin triangle with an apex opening angle of <40{\deg} that touches thecenter of the petroglyph symbol. The majority of the sun daggers use a spiralpetroglyph, with circles and other symbols being used. Where a spiral orcircular petroglyph has a coincidental light/shadow display, the false alarmrate is measured to be 20% to 33%. Sun daggers that have indicated declinationsother than +-23.4{\deg} or 0.0{\deg} are false alarms, including claims foralignments to cross-quarter days and lunar standstills, which are certainlywrong. Intentional sun daggers are not related to any form of calendricregulation, astronomical tools, or public ceremony. Rather, abundantethnographic evidence shows that sun daggers are a part of sites, called SunShrines, where a local Sun watcher would have lone vigils, with offerings andprayers to the gods on the solstices and equinoxes.

A Case Study of the Picture Rocks Sun Dagger, Plus a Review of the Intentionality of Sun Daggers