Every morning when I look at the regional map I see CW7408 (Mountain Center) is in the low to mid 30's. This must be an error in the weather equipment up there isn't it?
I took a look at this and was suspiction at first. If you follow this link you'll see this station appears to be on Lake Hemet. I can't imagine the sensor on the water, it must be right along the shore line. Depending on sensor location it could be effected by the lake.
Coincidently the family and I did some camping there over the Father's Day weekend and I can say it did get down to the lower 40's at night. I woke up about 45 minutes after sunrise and it was 44 degrees!
Another note…. Depending on sensor placement the lake would have a cooling effect during the day but warming effect overnight. The fact that it does drop so low overnight leads me to believe that its not on or near the water. Or it is still possible that, as you suggested, be an error!