Well, a small fold AND being able to go on a gravel road might be tough to find.
The MacLaren Techno XLR has a 65lb weight limit, the Aprica Cadence has a 70 lb weight limit, those are the highest I know of for "umbrella-type"/lighter strollers, but would not be much fun going on gravel with them. Also the Cadence is not really an umbrella fold--would probably be small enough but not sure as I haven't seen it in person. Of those 2 I would choose the XLR just because MacLarens are generally really good strollers.
I know the BJCE (Baby Jogger City Elite) has a 75lb weight limit, and I think that would be a good choice because of the terrain you want to use it on--but it is an AT so the fold is just not that small. You could pop off the wheels to make it smaller but you won't want to do that in and out of the car all the time. However, the fold is really easy, so that might work. I used to fit a Valco Tri-Mode (similar size to a BJCE, clunkier when folded) into an Audi A4 which is not much bigger than a Civic.
M, Mom to 3 handsome boys, '06, '08, '11