The Mauhúl valley is dotted with ancient ruins of a time when angels and their mortal allies battled an Abyssal invasion. Since that time, nobody has sought to build a settlement in this area. This is because of extreme measures taken, Mauhúl became a disease-ridden place of sickness and decay where only the hardiest of creatures can survive. For centuries, only plant-life existed here. Eventually, the animals that did manage survive and give offspring, gave rise to those of exceptional constitution, toughness, and strength; what some call Dire types. Theologians of Gimhak, particularly those following the god Naraz-Nâru, consider this "beast-only blessing" the work of the god Silvanus. They claim that it was his way of giving thanks to those that once fought alongside the Covenant and great commanders like Silvanus and Naraz-Nâru. There is another group on the other side of this thinking that said such perversion of the truth is said to discredit Silvanus, for he was neutral, father of the idea that nature should be left to take its course. They say if Silvanus was involved in this matter, then it was merely to enhance creatures to survive in a changed environment.
Mauhúl was a hotly contested area in the Demon Spawn War. This was because the highlands flanking it on the east, Bileddanul, are laden with mithril veins. The demon invaders were not interested in the resources, only that someone was in their way. The forces positioned here were Turkûn serving under then archangel Naraz-Nâru. His opposite were under the command of Ahnuthall; who in turn answered to Orcus. Facing the typical numerical superiority of their enemy, the Covenant decided to take extreme measures. There is no record of who gave the go, today's priests of Naraz-Nâru will tell you that their god was adamantly against it. He had warned his Covenant superiors, "the greatest risk is of it getting out of control, once it is in the wild, it is wild, no longer under our control." Even today, the use of disease to debilitate your enemies is often taken as a last resort. This is because of the unpredictability of diseases. The Covenant's deployment of RT-12 Leech ended up spreading to both armies. Because of its virulence, and for the rest of the war, neither side sought to hold the valley. Both retreated away from it. Ahnuthall went east to deal with a threat in the Bowkrak hills. Izanargam on the edge of disease-ridden valley, continued to supply ore and arms to Covenant soldiers for the rest of the war.
Oddly enough, today's Blighters got their start from the research that went into making the RT-12 Leech. Blighters, a bane to civilization today, had their beginning as a team of druids assisting alchemists developing a disease that would wreck havoc on their enemies. Since the agent they were working on could not be safely deployed in the enemy lines without risk of affecting their own, the research team came up with a way of melding RT-12 Leech into plants. This made it so that every season, during the plant's pollination time, the disease would be released onto the land around it. For whatever reason, Covenant decision-makers behind this germ warfare did not consider streams and brooks, and the Foronir river, and the movement of seeds from one area to another by birds and critters. Eventually, plants affected by the RT-12 Leech were taking root in and behind the Covenant strongholds dotting Mauhúl.
In the valley's southern parts, it is often wet and pocked with fog banks. In some areas, the fog is perpetual. This is most noticeable near the Idrongrun bog.