While driving up the grade, I noticed a large UFO going south towards the beach, 30 seconds later it disappeared in the east horizon

I was driving a friend home from my girlfriend’s house in Camarillo. While driving up the grade, a steep mountain on the 101 connecting Thousand Oaks to Camarillo, I noticed what I had assumed to be a plane also going over the mountain, south towards the beach. I began to realize that the craft was a lot larger, as well as closer, than I originally thought as we got higher up the mountain. As it got closer to the mountain, the lights on it shifted from being horizontal to diagonal. I told my friend that “I don’t think that was a plane next to us.” When we got over the grade I was excitedly pointing south towards the direction i saw it heading in, and she said she didn’t see anything. Then she said “oh, my god,” and pointed east. The lights were straightening out, and it very slowly disappeared over the Santa Monica Mountains- towards Lake Malibuo. Right after it had disappeared over the mountains we had noticed a plane flying above us towards the same direction. However, the lights on this one looked normal from below, it’s altitude was low, and it was flying in the same direction as the UFO. The only photo I have is of the plane flying away.