Intensive geological sampling and survey work of the pipeline route started in spring 1970. Aerial photographs were taken, examined, and a preliminary route was detailed.Mead, p. 177 Small survey parties physically visited the route and hammered stakes into the ground. The work was difficult; animal dangers forced the crews to be armed, and they also had to cope with the remote area and limited infrastructure. In places, the foliage was so dense that trees had to be cut down and progress was limited to per day.Mead, p. 178 The surveyed route passed through several mountain passes: Atigun Pass, Isabel Pass, Thompson Pass, and Keystone Canyon.Mead, p. 179 In the latter location, surveyors had to rappel down cliffs in order to perform their work.
