"The Invasion of the Lava Men"
In the aftermath of the fight between the Hulk and the Fantastic Four (Fantastic Four ((1961)) #26) in which the Avengers were embroiled, the Avengers survey the damage at the mansion, and go their separate ways to attend personal matters.
Rick Jones, having been spurned by the Hulk, now plays sidekick to Captain America. Soon, a terrible phenomenon is felt across America, and it brings the Avengers to investigate.
The Lava Men, last seen in their battle with Thor, are trying to expel a danger from their sub-surface world, a Living Rock which emits a deadly energy. They bring the Rock to the surface near the desert army base of General Thunderbolt Ross, where Doctor Bruce Banner is based.
There is dissent among the Lava people. Some suspect the King's advisor, the Witch Doctor, of wanting to goad the surface people into war.
Ultimately, the Hulk appears at the battle between the Lava Men and the Avengers, and he inadvertently strikes a blow to the Living Rock, causing it to implode. The catastrophe averted, all go their separate ways. 23 pages (X-652).
Reprinted in Avengers Annual #4.