strikes the outermost edge of it during the full "maximum moon", again in mid-winter. Fajada Butte bears five other petroglyphs—including a carving of a "rattlesnake", other spirals, and a rectangle—that are conspicuously lit by contrasts between sunbeams and shadows during equinoxes or solstices. Public access to the butte was curtailed when, in 1989, erosion from modern foot traffic was found to be responsible for one of the three screening slabs at the "Sun Dagger" site shifting out of its ancient position; the assemblage of stones has thus lost some of its former spatial and temporal precision as a solar and lunar calendar. In 1990 the screens were stabilized and placed under observation, but the wayward slab was not moved back into its original orientation. Alignments Some parties have advanced the theory that at least 12 of the 14 principal Chacoan complexes were sited and aligned in coordination, and that each was oriented along axes that mirrored the passing of the Sun and Moon at visually pivotal times. The first great house known to evince fastidious proportioning and alignment was Casa Rinconada: the twinned "T"-shaped portals of its radius great kiva were north–south collinear, and axes joining opposing windows passed within of its center. The great houses of Pueblo Bonito and Chetro Ketl were found by the "Solstice Project" and the U.S. National Geodetic Survey to be sited along a precisely east–west line, an axis that captures the passage of the equinox sun. The lines perpendicularly bisecting their principal walls are aligned north–south, implying a possible intent to mirror the equinox midday. Pueblo Alto and Tsin Kletsin are also north–south aligned. These two axes form an inverted cross when viewed from above; its northbound reach is extended another past Pueblo Alto by the ramrod-straight Great North Road, a pilgrimage route that modern-day Pueblo Indians believe to be an allusion to myths surrounding their arrival from the distant north. Two shared-latitude but diametrically opposed complexes, Pueblo Pintado and Kin Bineola, are located some from the core buildings of the central canyon. Each lies on a path from the central canyon that is collinear with the passage and setting of the full mid-winter "minimum moon", which recurs every 18.6 years. Two other complexes that are less distant from Pueblo Bonito, Una Vida and Peñasco Blanco, share an axis collinear with the passage of the full "maximum moon". The terms "minimum" and "maximum" refer