The Firey Hills
The firey hills are known for their tremendous heat and volcanic action, though they are mountains, they are called hills. This is for the small hills the build up gas makes inside of the ground. They push outward to be released and create small hills inside the mountain range.
The seeping gas is mildly poisonous and you can live through it, but too much exposure could cause lasting effects, and extreme exposure can even result in death.