I was driving late night to a campsite in a very rural part of the Big Island of [XXX] , about 45 minutes from where I live. I was by myself except for my dog, in the passenger seat. I was on a country road with a 30 mph speed limit, going about 25 mph. I engaged the cruise control and it immediately went up to 40-45 mph, far faster than the limit and far faster than was safe given the wet conditions and windy road. As I tried to slow the car down, using the steering while cruise control adjustment buttons, I steered through a curve and rather than turn with the road, as I had intended, the truck slid off the road to the left, effectively hydroplaning, into two trees, at about 40 mph. The airbags deployed as the truck came to a complete halt against the two trees. The car automatically called 911 as I sat there trying to assess what had just happened, whether I was hurt, and whether my dog was hurt. I told the 911 operator that the truck had called them automatically adn that I was ok and I would call in the morning after assessing what had happened. I am waiting for the police report and also waiting for the incident report from Rivian, which has an on-board log of events. I don't know why the cruise control engaged at such a high speed, rather than at the posted speed limit, but this appears to be a known flaw with Rivian's cruise control that I was not aware of. The cruise control and software are available for inspection by NHTSA. There is also an active recall on this