Leading up to the Crap Times, a number of people retreated into the wilds, hoping to find enough sustenance to survive. Many of those died as the irradiated magic continued its sporadic spread throughout the land, but some did survive. In particular, some who had retreated to the bounty of the massive Redwood forests peppering California and the Pacific coasts found that the trees seemed to offer them some protection from the wild magic of the Crap Times. It is a matter for legend whether the trees absorb, repel, or filter the magic, or if the trees are perhaps sentient themselves, or even if there's something more divine at play.
Over time, the people who took shelter in the trees found that their life span had extended, their features had softened, their minds were clearer and their hands more able. Some attributed the changes merely to one-ness with nature, while others believed the trees had changed them. Still others sought more rational explanations, wondering if small amounts of fallout were transforming them as well. Without the rest of humanity spreading its cities and razing the forests, the trees began to spread. The forests now cover most of the California coast, as well as a strip of the Sierra-Nevadas.
Elves are long-lived and feel a sense of protection, even chosen-ness, which tends to lead to an aloofness and arrogance. Most Elves believe that they are the bearers of truth and the proper order. They care for other post-humans, but see themselves as instructors, or older siblings, which many find to be patronizing. Many Elves aren't looking to rebuild in the Now What?, as they feel that they have already found the way and are merely needed to pass it on to others.
High Elves
Even more arrogant than their cousins, High Elves live in smallish Sequoia groves in the mountains. These communities were generally founded by Elves who felt they needed a retreat from the others over differences of opinion, often over the role of nature in their society. High Elves are more inclined to build structures, and more inclined to use magic for more than the protection of nature, than their cousins to the West. These massive trees proved even more effective at protecting them from the wild magic than the tall Redwoods, and the High Elves haven't changed much from their human ancestors. Most Half-Elves come from High Elf stock, as they are the sub-race most likely to interact with other humans and post-humans.
Wood Elves
While all Elves retreated into the protection of nature, and in particular, the curious magic-channeling safety of the Redwoods, the Wood Elves viewed this as a particularly spiritual protection. These Elves continue to inhabit exclusively the branches of the massive trees, and view themselves as these forests' protectors as much as the other way around. They embrace magic or technology when used to enhance or protect nature, and reject any that is used for destruction. Wood Elves believe that the Crap Times were the inevitable result of a disconnect from the natural world, and the only way to prevent another cataclysm is to become more in-tune with the world as it was. Their domain is a huge, contiguous strip of forest along the West coast, which many never leave. It is impossible to say how populous the area is, as they tend to leave no trace of their presence.
Dark Elves
As the forests returned and spread, the Dark Elves were communities that formed out of a feeling of 'outsider-ness' among the Elves. They saw that the trees protected them from the Crap Times, but they didn't view sanctification of nature as the appropriate reaction. Rather, they sought to understand the why of it all, with an almost scientific curiosity. They began to view their cousins' emphasis on life as perverse, and recognized themselves that death was as natural as life. When the initial waves of arcane fallout had subsided, they moved into caves near their cousins' mighty groves to continue exploring uses of magic that were considered obscene to the nature-loving breeds. Away from the protection of the trees, the Dark Elves began to adapt to their new environments quickly, with their eyes becoming more astute in the darkness and their skin darkening to better camouflage themselves. Additionally, as the Crap Times came to a close, the magic permeated them, giving them natural magic which aided their survival in the underground.