Pinnacles is a cut region east of Highway 97. You cannot enter it; both ways in are blocked. Data miners found plans for a sixth camp, Fort Klamath, ranches and farms there, plus a cut Act 4 mission.
No. The two routes into Pinnacles are blocked, and only a rough prototype of the region was ever built.
It likely comes from the tall volcanic spires in the southeast of Crater Lake National Park.
Image: Bend Studio / PlayStationBelknap
Belknap is the volcanic region south of the Cascade, home to Ada Tucker's Hot Springs camp and the town of Marion Forks. You come here early for Tucker's work and stay for its seven Hordes and three infestations.
Cascade
Cascade is the northern starting region, in the Farewell wilderness around Copeland's Camp at Peaceful Lake. It is where you learn the game, and it still has 8 Hordes and 4 NERO research sites to come back for.
Crater Lake
Crater Lake is the far southern region built around the real lake and Wizard Island, the Militia's headquarters. It opens in the second half of the story and has the most encampment jobs and NERO research sites in the game.
Highway 97
Highway 97 is the southern stretch of US highway running through Chemult and past Chemult Community College. It has more Hordes than any other region, including the 300-strong Lobert Draw Ridge Horde, so bring your best gear.