Yes - it is normal for lizards to sit on each other.
I'm not sure what the mating season is, but I think it is march to july.

The ones you have look like San Diego subspecies.
I don't know what their clutches are like - if they are like California subspecies - adult females tend to have 10-16 eggs.
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3.6 L. getula californiae (Cal. King)
1.1 L. getula nigrita (MBK)
1.0 Pantherophis guttatus guttatus (Corn)
1.0 Thamnophis sirtalis fitchi (Valley Garter)
1.0 Boa constrictor constrictor (suriname, fostering/rescue)
3.3 Elgaria multicarinata multicarinata (Cal. Alligator Lizard)