Joseph and I went to this last weekend. We were two of about 50 volunteers. It takes a lot of people to run one of these! We had a great time, staying at Motel 6 in Lodi on Saturday night.
A Combined Driving Event is like a Combined Training Event before they took out the Roads and Track part of the Cross Country phase.
Dressage is dressage but the arena is 40x100 meters instead of 20x60 meters.
Instead of cross country jumps. they have obstacles that are like mini-mazes. You have to go through each part in the correct order and in the correct direction. Each obstacle gets timed.
The jumping on the third day is replaced by a cones course, with gates made of two cones a precise distance apart. Each cone has a ball on it, so if the wheels even jostle the cone a little bit, the ball falls off.
Volunteering at horse shows is a great way to participate without loading up the horse and all the stuff!