Mammoth is typically open before thanksgiving as I believe they full up a couple park runs with man made. Bear as well fills up a couple park runs with man made but because they have a lower elevation it really depends on the temps. Best time to hit those places up in early season is 2nd week of december. I typically hit them up in nov and its nothing special. I strongly suggest if you go to bear wait until January and go during the week. The red bull park and the scene are too epic to miss if its your 1st time at bear.