I used to mtb alone at a state park up in MA. It was close to my house, not too technical, and fairly well-travelled by others, so I felt reasonably safe there. I have not mtb'd by myself since moving down to MD, again..for the reasons you cited. I will (strangely?) road bike on my own, however, although get bored to tears with anything longer than about 35 miles.
2007 Seven ID8 - Bontrager InForm
2003 Klein Palomino - Terry Firefly (?)
2010 Seven Cafe Racer - Bontrager InForm
2008 Cervelo P2C - Adamo Prologue Saddle