For an idea what common towing speeds are in CA keep an eye on the big rigs in the area you're in. I will say they're generally above 55 on roads where it is safe. There seems to be local custom in the area for enforcement but common here in so. CA is 60-62. Of course on winding mountain roads, even the 55 MPH limit may be too fast.
The one I had to watch the most is small low profile ATV trailers. Very easy to look down and see 70 MPH on the speedometer. And that is generally a quick ticket when caught.
