One of the most popular theories proposed for the purpose of the glyphs is that they are solstice markers or some kind of ancient calendar.

While there are clear indications that the ancient inhabitants of the southwest were accomplished astronomers, including the much publicized discoveries in Chaco Canyon and in Central Texas, the research team does not feel that this is a valid theory as to their intended use.

To date, more than 120 glyphs (of the 370+ total found) have been located, within negligible deviation from 37°00'04" latitude, pointing to more than 90 different compass azimuths ranging from 0° to 359°.

Although the team does not rule out the possibility that the glyphs may have some calendarical significance, (perhaps lunar instead of solar),  current data would suggest  this theory appears is invalid.

Understanding basic principals of solstices is pretty simple:

The Earth is actually nearer the sun in January than it is in June, [by three million miles] , and  our Earth leans slightly on its axis,  23 degrees and 27 minutes off perpendicular to the plane of it's orbit.
 

As the Earth orbits the Sun at this odd angle, the Sun appears to "move" northward or southward in the sky.

  "Solstice" actually means "Sun-stands-still"

More precisely, it is the point in Earth's orbit around the sun at which this apparent movement stops ... and changes direction.

This is an important fundamental principal because the apparent movement of the Sun is relative to your position on the surface of the earth.  However, this relative movement is negligible if your position on the earth, or degrees Latitude from the equator, does not change.

These 120 glyphs have been found over a 5,000 square mile area, and their latitude never varies more than 20 miles from 37°00'04" latitude, which for the purposes refuting the solstice theory as the primary function of the marks, is a negligible deviation.