The Architects of the Mountain

Like many striking geographical features, the Molehill Mountains are surrounded in myth about their creation and about the mysterious secrets they may hide in their hard-to-reach sections. One of the most striking of the myths that surrounds the towering mountains is the myth of their creation, and of the genesis of their vast caves. The mountains make such a good home for those who are willing to make their lives at high altitude because they are so permeated with pre-existing caverns, the most notable being the ones in which the dwarves have built their cities.

Summary

The myth, still widely believed and spread in dwarven culture, is that the dwarven god, seeking a place to make a home for his people, created a great mountain from which water flowed, and which teemed with life. Despite these many natural blessings, the god of the dwarves knew that the mountain was also a dangerous place. Winds fly with wild speed around the peaks, and sheer drops threaten those with unsteady hands. Knowing that his people would not survive alone on a mountain top, he created a species of giant mole, with claws of adamantine and coats of gold. These legendary creatures are supposed to have been the teachers for these first dwarves, and taught them how to make their homes underground, in tunnels and caves. 
Despite the intent of their creator, the moles were eventually unsatisfied with the way that their students dug carefully, distracted by glittering gold and gemstones. Unhindered by eyes with which to see these riches, the moles dug with a passion for expansion, and were soon lost to the dwarves deep underground. Many dwarven explorers and religious folk have gone hunting to find the moles. The tunnels, however, shaped long ago by masters from which the dwarves never learned all there was to learn, are esoteric and winding. Many of them seem to have shrunken down into tiny gaps and cracks in the walls, and the mountain below a certain depth quickly transforms into a labyrinth from which many have never returned.
Many dwarven preachers believe that finding the moles once more would unlock new secrets of the mountains to the dwarves, completing their education.

Historical Basis

Those with a less religious lens have often examined this myth with scrutiny. Surely, the dwarves simple came upon the mountain and dug the caverns themselves. Perhaps, they posit, the caves were actually dug by dragons, seeing as how the myth describes creatures with massive claws and a golden shell. This is considered a great insult by the dwarven people, who hate dragons with a passion. 
Believers in the Architects have often pointed out sections of cavern with large straight divots in the stone, claiming these to be claw-marks left behind by the architects to guide the dwarven people to their destiny below. Indeed, these marks are compelling evidence, though individuals who have attempted to decipher what they might mean, or how they might serve as a guide, have either become hopelessly lost or simple given up.
Other individuals, generally, nobles, hold artifacts in the form of long needles of gold which they claim to be tufts of hard golden fur belonging to the original Architects, passed down in their families for generations. Some even hang massively heavy adamantine "claws" from their mantles, claiming that the Architects would sometimes shed their metal claws and grow new ones, leaving their incredible powerful digging tools to their dwarven students.
To some, the existence of these markings and artifacts is proof enough. To others, these simple look like extremely expensive ways to perpetuate an important religious myth.

Spread

The myth is taught to all young dwarves who grow up in the Molehill Mountains, to stoke their sense of adventure and teach why the dwarves continue to delve beneath the earth. It brings wealth, of course, but it also serves as an honorable task. The dwarven religion reveres explorers of caves and miners, and often offers affordable magical healing for conditions brought about through mining or delving into deep caves.

Variations & Mutation

The dwarves' strong sense of tradition and unity has prevented from much in the way of variations of the myth. There are versions of the story which change in small ways. Some small sects observe that the moles may have closed their tunnels not because they were challenging the dwarves to follow, but because they were warning them of dangers beneath. After all, a claw mark on a tree in nature can often indicate to other animals that they should not venture into a territory, not that they should eagerly stroll into a predator's lair.

In Art

Many dwarven reliefs and statues depict the architects, leading the dwarves deeper. Religious reliefs often contain three tiers. In the sky, the dwarven god watches over his people, molding them stronger and more capable with each generation, in the earth, the dwarves delve deeply. Deep beneath the earth, the moles wait in their expansive tunnels, discovering treasures and secrets to share with their students, the dwarves.