The Grotto Caves Horde is a 75-Swarmer Horde Killer target that hibernates in the Grotto caves in the Cascade. It opens after Lots of Sick People and pays Copeland's Camp.
Bring several Molotovs or napalm, a couple of bombs and full ammo. Pick a chokepoint and a retreat route before the first shot, and use Focus on the front runners. Meet it at the cave mouth with fire as it comes out.
Hordes rest in their hibernation spot during the day and go out to feed and drink after dark. Hitting a sleeping Horde lets you set up traps first. Every Swarmer drops an ear, so loot the field afterward for the bounty collector.
It becomes a Horde Killer target after Lots of Sick People.
Deacon says hearing about this Horde gave him the idea of sealing caves to stop Hordes hibernating.
Cascade Highway Horde
The Cascade Highway Horde is a 50-Swarmer Horde Killer target along the Santiam Highway near the logging camp. It opens after We've All Done Things and clears one of Deacon and Boozer's old danger spots.
Death Train Horde
The Death Train Horde is a 50-Swarmer Horde Killer target in the Cascade, named for NERO's body trains. It opens after Drifters on the Mountain and pays Copeland's Camp.
Horse Lake Horde
The Horse Lake Horde is a 25-Swarmer Horde Killer target near the Caldera Hydro Dam reservoir in the Cascade. It is one of the smallest Hordes in the game and a good first try.
Little Bear Lake Horde
The Little Bear Lake Horde is a 30-Swarmer Horde Killer target in the Cascade that often blocks the old Belknap Tunnel route. It opens after We've All Done Things and is an easy one to start with.