Red dots are fatal crashes, every one in California from 2020–2024, any vehicle and anyone killed: people in cars, on foot, on bikes and on motorcycles. They come from NHTSA's FARS, the federal count of fatal crashes, which places nearly every one, freeways included.
The smaller dots are intersections with 5 or more crashes reported within 100 ft of where the two streets meet, 2021–2025, from the state's police reports (CCRS). Freeways are left out of these. Where a report has no coordinates (Los Angeles and San Francisco police leave them out), the corner is placed from the street names on OpenStreetMap.
These are counts, not a measure of risk. A busy corner has more crashes because more people drive through it, and there are no counts of how many do.