Quite simply, it was easy due to the thousands of naturally occurring oil seeps (This is where the subsurface oil migrates to the surface and is expelled onto the ground) Local lakes come with a natural oil slick due to subsurface seeps. The Natives at Kaktovic have been harvesting and burning pieces of oil soaked tundra since pre-history. They have also taken advantage of an occasional easy meal when caribou get trapped in the mini tar pits near the coast. The land literally bleeds oil. I guarantee that Mother Nature has spread more oil contamination on the Alaskan North Slope than man's petroleum development ever will.