Here is a searchable database of summer research programs.
I ran a quick search for biology/medicine/neuroscience + chemistry for HS students and got 36 hits.
The largest number of California results were for the MESA programs at various Cal States. In order to participate in MESA, your child must attend certain designated partner high schools.
MESA seems to be more focused on mathematics and engineering than biological sciences, but it might be worth a look if your child’s HS participates in the program.
MESA info here: https://mesa.ucop.edu/student/
Harvey Mudd is part of the Summer Science Program (SSP) consortia
SSP accepts about 400 students nationally and sends them to 10 different university campus.
As mentioned above, you’ll need to check to see if these programs are still in existence since the major cuts in NIH funding have shuttered so many research and science outreach programs.