I was working as a carpenter during the construction of the Taft prison in California in 1990. One morning, as I was driving westbound to work on HWY 119, I noticed a bright light that seemed out of place hovering over the horizon. I didn't think much about it until something strange happened. A circle formed around the light (UFO) and, within the circle, the sky lit up like it was day time, but this was about 30-45 minutes before sunrise. The entire sky was dark except for this UFO and the small circle that formed around it. I pulled off to the side of the road to get out of my car and take a closer look; I noticed 5-6 other drivers doing the same. After 5-10 minutes, the UFO slowly descended to the bottom of the circle (force field) that surrounded it. The UFO didn't just pass through the bottom of this force field, it looked as if it pierced the circle (force field) actually pulling it down into a point before it seemingly "broke through" and flew off southbound towards Los Angeles. Once the sun finally came up, as I arrived to work, I noticed strange squiggly lines in the sky. I checked the newspaper and watched the evening news over the next few days to see if there were any explanations for this strange encounter, but I found none. I've never seen anything like it before or since.