I think Bob Bledsaw's intent was that the dwarves arrived on the planet along with the other Elder Races over 40,000 years ago.
This history also mentions the Great Dispersal, when races spread throughout the land around 12,000 years ago.
The rumored dwarven ruins in the Valley of the Ancients might be a reference to this:
Bob Bledsaw Wrote:After 133 years of exploration and exploitation efforts, a robominer tunneled into a large cavern containing dragons and humanoids. War immediately insued.
The First Men attacked upon the backs of dragons.
...which would have been around 44,600 BCCC.
Anyway, for the purposes of getting the Wilderlands and Blackmoor timelines to talk nicely to each other, probably events tens of thousands of years ago aren't the most salient. I think the fall of the Majestic Fastness is the most notable recent event in Wilderlands dwarf history, and it's around the right time (that and the orc horde of 3983) for it to have influenced Khazakhum.
LoZompatore suggested placing the discovery of the Forges of Power described in CM6 in 7000 BC in the Mystara calendar, or around -2000 in the Blackmoor calendar, or about 1400 BCCC in the Wilderlands timeline. The first Forges of Power coincided with the dwarven discovery of how to work iron, which would be earlier than they discovered this in James Mishler's Blackmoor timeline.
I'll just overlay the dates on
James Mishler's Age of Blackmoor directly onto the Wilderlands dates and see what happens (I'm assuming 4000 BC=1000=4400 BCCC).
10,000 through 8,000 BC. The dwarves, an offshoot of the brute-men race, lived in the hills and mountains of the continent of Brun; they were not, at this time, a subterranean race. By this time they had already domesticated the goat and the dog. (Mishler)
8,000 through 6,000 BC. The dwarves had by this time domesticated numerous plants, most importantly barley, which became the staple of their diet (as bread and beer). (Mishler)
7,000 BC. The dwarves discover the
Forges of Power. (LoZompatore)
6,000 through 5,500 BC. The dwarves had discovered bronze (either independently or from the giants), and with a burgeoning population, many dwarven clans began migrating out from their ancient homeland. A fair number of dwarven clans reached Skothar, where they settled in and around the mountains in the north, where the only major tin deposits on the continent were found. (Mishler)
5,500 through 5,000 BC. In 5500 BC chromatic dragons, huge powerful beings from another galaxy, arrived on Brun in the lands inhabited by the dwarves and decimated the dwarven civilization (which lay in and around the "Wyrmsteeth Range"). The dwarves of Brun had been decimated and enslaved by the chromatic dragons; the only remaining free dwarven lands were found on Skothar, to which a very few dwarves from Brun were able to flee with their tale. The dwarves of Skothar, hoping to assist their brethren on Brun, began developing new weapon technologies with which to combat the draconian menace, as the scales of the dragons were more than a match for the bronze weaponry of the dwarves. The dwarves developed Iron, which was rather more capable than Bronze of dealing with the tough armor of the dragons. (Mishler)
5,325 BC. City State of the Invincible Overlord founded by unification of nomad tribes and dwarves. (Wilderlands Player's Guide)
4,875 BC. Dwarven hero, Ubestar Kazakhum is born (DA1).
4,500 BC. Ubestar Kazakhum establishes the Northern Delving mines, in the Crystal Peaks mountains. It is said that these mines are the most prominent example of dwarven architecture throughout the world (DA1).
4,417 BC. Trade between the dwarves and Modron is cut off by an orc horde. (Wilderlands Player's Guide)
4,400 BC. The Majestic Fastness is invaded by the dragon Analegorn and his young, driving out the dwarves there. The dwarves venture to the Sunstone Caverns to the north and drive out the local beastmen (gnolls), founding Thunderhold. (Wilderlands Player's Guide)
The last three dates could be brought closer together, I think, or Ubestar Kazakhum's colony could be unrelated to those events.
I don't see any direct reference to dwarves in the descriptions of the Elder Races, the Uttermost War, or the Great Dispersal (or really anything prior to the foundation of the City State) so dwarves could be assumed to have come to the Wilderlands later, around the time Mishler suggested as the time of the dwarven migration from Brun to Skothar.