... as well as the rest of the world:
Go to "explore"->"activities", click on the layers icon in the top left corner of the map, choose "heatmap"->"cycling".
Curious map. In San Diego, main features are in agreement with my observations: hugely busy north-south 101 corridor from UCSD to Oceanside, and, to lesser extent, from UCSD to Mission Beach; a lot of traffic on the 56 bike path; and a general lack of activity north of 78 and east of 15. In North County, Elfin Forest / Harmony Grove / Del Dios loop seems pretty busy, and there are apparently so many mountain bikers in the canyon north of Mira Mesa that their trails show up on this generally street-oriented map.
In the LA area, you can practically draw a map of good and bad neighborhoods by looking at the heat map. It's curious how OC cyclists sharply disappear north of 55, or that there's a lot of coastal traffic south from Long Beach and north from Rancho Palos Verdes, but virtually none connecting the two (barely 5 miles away from each other.)