We just went through this because our Reflection's GVWR was more than 10,000. My husband made appointment with both DMV and Highway Patrol,so he would have all the facts correct. These are the facts in CA: if you tow a 5th wheel that has a
GVWR over 10,000 lbs but not more than 15,000
GVWR you must have a license that includes an "Endorsement" If you don't have that endorsement and you are in an accident you may find that your insurance won't cover damages,and you will be cited by CHP. And here is the important part and where HP helped us more than DMV......a lot of DMV clerks are not aware of this law and may give you inaccurate info.If they tell you you don't need it they are mistaken. It is in the DMV book of regulations for towing but you must read
entire section on 5th wheel requirements to get to endorsement section. CHP and insurances know about it -even if DMV clerks are foggy

and ignorance of the law for the person towing is not an acceptable excuse.
This is what is required for the drivers license with "endorsement" - you have to take a regular drivers test for a Class C license, unless you took one within last year. You must also take a second test, which is the one that asks questions about your knowledge of RV rules of the road. My DH got the booklet- for RV rules of the road-ahead of time,and studied the booklet before taking the test. He said it wasn't difficult and for the most part contained questions that any person towing a 5th wheel would know,but he was glad he studied. He made appointment, took the test. He passed. They took his picture, took his money for new license (33.00 ) and told him they would mail this new license. If you drive in CA but live in another state that doesn't require this endorsement you are fine,it's only if your state requires it.
Just to stress - some DMV clerks were confused about this law. We knew that ahead of time so DH took rules for towing 10,000-15,000 GVWR with him. They saw it in black and white. They had to find a person in DMV who knew what to do and that is how they proceeded from there. We live in small town so perhaps clerks in larger office are more knowledgeable about this law. One way or another ....whether they know about it or not, it is the law! And the person responsible for towing has to know that! Hope this helps anyone in CA. Very glad we checked with CHP and insurance! One last thing...you don't have to take a driving test...just written test.