An array of green pulsing light that condensed into a mass object

Headed to work as usual headed down Hwy 2, just passed the last house before you start heading up the east side of Stevens pass. As I approach the grade heading up Rayrock, an intense green light array appeared and started pulsing. It was just above the tree tops and probably was the length of a football field. The light was flat on the bottom, but it projected upward in an irregular pattern. Then it sudden condensed into a roundish mass of green light, and slowly traveled parallel with the ground. I had a visual for about 3-4 seconds, but due to the topography in that area it went out of sight. At first I thought it was a transformer that exploded but there is no overhead power in that area. It was crystal clear out and the stars where visible.