https://www.dges.org/history
The best we can tell is Devil's Gulch got the name well before the ranch was formed. Devil's Gulch was the passageway between Nicasio Valley and Paper Mill Creek. The local history seems to indicate that the gulch got its name because of how treacherous this important trail was. In 1864 Devil's Gulch Ranch (873 acres) split off from a larger parcel and was purchased by two Martinelli Brothers, Union Army Civil War officers using their wages to start fresh in California.
eta:
I've seen this trail twice described as nothing like it's name. For example:
(By the way, don't let the Devil's Gulch name scare you. For years, every time I passed this sign, I envisioned a harsh, steep climb through dry, hellish terrain. After all, they got Mount Diablo's name right. Instead, Devil's Gulch is a gentle, relaxing saunter through grasslands and alongside a peaceful creek. I would love to know the origin of the name.) In the summer, and on weekends, expect a lot of horse traffic. In the winter when the weather is chilly, you may have the trails to yourself, especially on weekday mornings.
This
3.9 mile out and back hike is easy, with about 880 feet in elevation change (mostly in small increments).
Exposure:
Mostly shaded.
https://bahiker.com/northbayhikes/sptdevil.html
Personally... I've never visited so I don't know.