As of Monday, 90 COVID-19 patients were hospitalized in Ventura County and 30 were in intensive care.
Some hospitals reported they have exceeded their emergency room capacity.
Plans for a surge have been in place for weeks in case it happens.
Ventura County officials said last weekend's Fourth of July gatherings could possibly lead to more hospitalized patients.
"Early on when people wanted to open things up and people were interested in loosening restrictions over and over again I heard them say 'our hospitals are empty,' and now we're in quite the opposite position, our hospitals are very full," said Dr. John Fankhauser, CEO of Ventura County Medical Center.
Officials are urging residents to wear a face covering whenever they are in public and practice physical distancing.
EPA approves 2 Lysol products as first to effectively kill novel coronavirus on surfaces