Saw dark diamond shaped UFO for 1 and a half minutes at tree top level.

While driving up Sherwood Road going outside of Willits California, the driver (Jeff) saw something weird as we cressed the top of Sherwood by the cross.
 As we traveled about 50 yards, the driver decided to pull over and I do not know if the car stopped running or if it was on his own accord, the passenger (Martha) saw the object too. We exited the vehicle (a 1979 Datsun 210) which is when I saw the object moving across the sky. I previously was in the back seat and could not see what the others could see.
 The object we saw moved very slow, about 15 miles an hour, and did not have much sound to it. It was at tree top level (about 100 to no more than 150 feet above) Lights shot from the pointed end to the back of the object and then again to the forward point in different colors. It made a low humming sound.
 As it passed over us, we manuvured around the tree's, backtracking from where we had come from to get a better view of the object. We then ran to see it from around the tree's and the object had now dissapeared.
 Cars were now coming and we ran back to our car, jumped in, and left the sight area. None of us ever forgot that experience.
Witness indicates that the date of the sighting is approximate.  PD