All the structures mentioned above are theorized to have been used in astronomical observations.
The Stonehenge has been said to have been built by a lost civilization and was either a burial ground or an observatory as suggested by the circular stone embankment surrounding the structure.
The Sun Dagger or Fajada Butte is a more debated structure as it does not match with the building patterns of the Chaco people. Those who theorize its astronomical use say that it predicts solstices and equinoxes.
The Bighorn Medicine Wheel is peculiar as its historical knowledge is literally zero. The only reason it fits the common thread is that it looks like a sundial and hence might be a clock.