From my home in San Clemente (mainland) many years ago, on a very clear day and before all the trees blocked the view, San Clemente Island was a bump on the horizon. And Catalina looked like you could swim to it.
The Coast Guard has stepped up patrols between San Diego, the Coronado Islands and San Clemente to intercept illegal aliens being smuggled by boats. We can see San Clemente on clear winter days and there is a USCG presence most days out there. A C130 from Sacramento was also just involved in a SAR rescue of a yacht in the yacht race to Cabo. The average day sees a number of marine and navy helo’s transiting the area at low level. Sounds like a c-130 SAR mission tangled with a transiting helo.