The majority of the race takes place on the beautiful Silverado Trail, which runs along the eastern edge of the beautiful Napa Valley. Unlike the "Napa"-named triathlons which take place up in Lake Berryessa, the "Napa Valley Marathon" actually takes place in the Napa Valley.
There's about 837 ft. of incline along the course, nothing crazy though. Overall there's a negative elevation from start to finish.
I would characterize the course as mostly very, very slow rollers with alot of flats.