Canyons are really large and common surface biomes that you can find rather easily. Still you might have to swim across larger bodies of water for that, depending where you have started.
You will recognize Canyon-biomes from afar easily as they feature very tall bizarrely shaped pillars and formations of rocks colored with horizontal "stripes".
Basically there are two kinds of Canyons, which can sometimes blend into each other. One type has snow-covered peaks with small rather bushlike Ashenwood-trees and/or Cragwood-trees on top, and some canyons of this kind can be all snow-clad from top to bottom with icy rivers/waters even.
Keep in mind not to walk on Snow for too long, as this can fill the freeze scale and result in cold damage over time, unless you take your time to warm up before that by creating a warm spot, like by placing at least 3 torches on the ground (not on solid snow nor ice of course) and standing on one of these.
The other - more common - type of Canyons is located in a bit warmer climate zones and usually doesn't feature any snow, while trees are also rare there. A few Canyons might also have rocky steep cliffs made of ordinary Stone, especially at their outward borders.
Canyons are made of different layers of rocks, often with Canyon Floor on their base, followed by layers of Sandstone, Dark Canyonstone, Ruddy Canyonstone, then caramel ordinary Canyonstone further up, and sometimes a bit of simple Dirt with Weeds growing on the very top.
It's advisable to fetch a few blocks of caramel-colored striped Canyonstone from higher up because taking it will start to unlock a number of crafting-recipes made from different Canyon-rocks. Mind that for mining these rocks, Stone Mining Cells will be needed! The same goes for Dark Canyonstone and Ruddy Canyonstone, not for Sandstone - this soft rock does not need any Power Cell to be mined.
Other than Mountains, Canyons usually do not feature any visible Nodes of Ore on the surface. However beware of the Caves, as in the Canyons a number of those have deep chasms inside that might lead to a deadly fall of careless adventurers!
As for animals, Dustevils can spawn on any kind of Canyonstone and/or Sandstone (even in older worlds before Canyon-biomes were introduced) during the (ingame-)day. Also Trogs and Dried Leafies can occasionally spawn in Canyons under the sun. Night Leafies can be met during the (ingame-)night.
Wood Treasure Chests can occasionally show up during (ingame-)night-times in dark places in range of view of player-characters in this biome. These valuable findings can also spawn very high up and/or at cave-entrances.