Answer: Without seeing the pest, it's impossible for me to positively identify it, but your description leads me to believe they are grubs - the larval stage of beetles - either June beetles or Japanese beetles. Why not collect a few and take them to your local nursery or cooperative extension office for positive identification? Helpful folks there can also make control recommendations. Master Gardeners typically hold plant diagnostic clinics at the main branch of the Huntington Beach Library on Saturdays (be sure to check before carting your insect pests to the library!)
Best wishes with your garden!
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