Access to this campground is so easy, whether it's by car or by bike. I have bikepacked here a couple times now; once biking up Highway 39 from Azusa (after taking the Metro Gold Line to Azusa), and once driving up the 39 with bikes and bags in the trunk.
The trailhead to the campground is impossible to miss, as it is marked by a large parking lot and a sign marked "Cogswell Dam". This campground is so perfect for bikepacking novices or those looking to do a gear check because it's an honest 6.5 miles of a relatively flat paved road. If you're trying to bikefish (it's a thing), this road is lined with fishing platforms for all sorts of trout, as the road follows a river the entire way.
The campsite itself is relatively large, with two vault toilets and two bear-safe trash cans. There are at least 5 campsites with picnic tables The river lining the road to the campsite is very accessible, and is perfect as a water source, or washing camp dishes.
While bugs are an inevitable aspect of being outdoors, the biting gnats and/or mosquitos are very formidable in the summer. We had some "natural" bug spray that had little to no effect, so you might want to bring your bug repellant A-game if bugs bother you.
Overall this campground is near and dear to my heart as it was my first bikepacking experience. If you're looking to introduce a bunch of friends to bikepacking, or backpacking, bikefishing, fishpacking (?), then this is the place to do it.