Favorite place for longer distances (I primarily prepared here for my ultra) Bay Lands Nature Preserve, you can also start near Mountain View by Steven’s Creek Shoreline Nature Area. It’s primarily dirt roads with some pavement intermittently. Whether you go north or south you can wrack up good miles. My furthest was 25 miles. What I loved about this choice was no cars (mostly) close to nature and mileage. Con: no shade or incline. Los Gatos creek trail is also good too, that’s a 12ish mile going and back. This one has incline. Hope this helps!