Hawkins paper is chiefly valuable for detailed large-scale photogrammetric plans of both Stonehenge and Callanish - the only Callanish plan with contours
The full reference is :

Hawkins, G., 1971 'Photogrammetric Survey of Stonehenge and Callanish'
in a volume entitled 'National Geographic Society Research Reports 1965'; NGS, Washington D.C.

The criminal thing is that, while he had an aerial survey being made of Callanish, they did FIVE other sites in the area as well. The photogrammetry was never done and when I went back to the survey company years later, they had destroyed the original photos and data.