I am from North San Diego.
My regular running places used to be...
Anywhere in South La Jolla to Jetty st in PB to Riviera or the end of the trail via the bayshore....by campland by the bay, etc....good for 10-14 miles.
Oceanside....strand...harbor...strand.....Carlsbad beach strand harbor strand end....about 11 or so. Flat.
Lake Hodges trails, starting in Rancho Bernardo Park...
Guajome Park, Vista.....many trails....
And my favorite...Double Peak....San Marcos. Elevation is perfect. Start at San Elijo Park. Turn on Double Peak rd. Net elevation is zero. Original elevation gain may be 800-900 feet within a couple of miles.
Not sure what is safe or open during the pandemic but when it's safe, these are good.