Herd of the Gusty Wilds
Hurray for Dartmoor, Newforest and Shetland Pony territory, the two former of which I actually know fairly well! Yes, I know it's not typical territory anywhere, but moorland's about 0.7% of the Earth's surface, and I think about 20% of that's in the UK, mostly because saxons were awful at just not deforesting things, so... yes the Brit's having a moor.
Territory
The Herd of the Gusty Wilds is on a sloped section of land. Most of their territory is on moorland fairly high up, with undulations of slope, and sudden massive rocky outcroppings. Some of the hills on the moor are simply enormous, which is advantageous to only the most sure-footed of the horses. The Eastern side of the territory lowers slowly through a lightly forested area onto a flat plain that stretches down to a long series of sand dunes, and then to the sea/a large water body of sorts. Within this low land section are a few marshy areas, with tall trees that can easily shelter horses. The territory entirely contains a few fleshy-footed settlements, within the moorlands, but the fleshy-feet always seem too preoccupied with their cows to do much horse-capturing as long as the herd keeps plenty of distance. There are some marshy areas within the moors where water pools during rain, and then floods out to form sudden rivers and streams across the plains below. They're very rarely severe enough to cause actual damage to any of the trees, but they can definitely make traversing the territory difficult.
Borders
The Eastern border stretches along a long stretch of sand dunes and a huge water body (I don't care if it's the sea or a lake or just a huge river. One of those). The other borders are very poorly defined, and the horses are essentially willing to go as far as they can before encountering other herds along them. Generally, they end after descents on either side, however. They are proud to have a large territory, but really they need it because of all the prickly moorland plants that reduce the quantities of grass available.
Prestige
The Herd of the Gusty Wilds are almost entirely descended from the accidentally released horses of the early settlers to the USA; they are proud warriors, and fierce fighters. Really, they could have been a very intimidating herd, if it weren't for the subtle adaptations that Moorland dwellers need.
One of the benefits for them of living in moors is that they have developed a sort of impermeability to the pains of the various spiky, annoying plants they encounter. It allows them to both boast of being thick skinned enough to not feel pain, and to cause trespassers pain by luring them into bushes, often done by feigning a retreat. Of course, they don't see it as a disgrace to feign retreat; one of the most glorious of their French ancestor's victories was one by feigning defeat!
While they would like to have a reputation to match their proud heritage, many herds just don't see them that way. They have a good sense of chivalry, and a lost foal will always be treated by the herd like one of their own until their mother returns.
The Gusty Wilds horses only believe in the Night Sky herd in a very vague sense; that it's a brief stopping point for dead warriors before they can be reborn to run again. They often name foals after recently deceased relatives who looked similar, believing them to be reincarnations, but naming a foal after a currently surviving relative is taboo, as they believe that the soul will be confused and both horses might die. They also believe that some souls will refrain from returning to run again for a few seasons or a few years, and this is all that the Night Sky herd are when they give signs. Beyond this, they have no real religious beliefs.
History
As stated, they are descended from the horses of early settlers to the USA, mostly the Spanish horses, but also some French horses. The first main body of them arrived after a ship containing horses ran aground. A decent number also joined the herds after the Spanish introduced one of the local native american tribes to horses, and they became horse-herders and riders themselves, which, of course, initially decreased their numbers, but then the fleshy-feet started fighting each other and a good number of horses became free. Those that did travelled into the higher land, where the fleshy-feet would not or could not follow.
Looks
Gusty Moor horses are descended from horses that often had very decorated or pale colourings. Their adaptations to the moorland environment have favoured them keeping broken-coloured coats, but gaining darker coloured fur; of course, many have light coloured coats, still, but those that do generally have patterning in other colours on top. The cold air and mist that comes with moorland territories has selected for longer fur than in many other areas of similar latitude. Because of living close to a large water body and marshes, they have not become quite so small and short as other specialised herds of their type. The counter-balancing pressures of needing to keep their mobility in water, but also of needing to be able to escape fleshy-feet through the moorland plants so that horses cannot be seen, and of reduced food density in the higher areas has reduced selection pressure for size, so horses of many sizes are welcome. It can be a surprise for outsiders that there are so many horses that might even be seen as ponies among the ranks of a proud ex-warrior herd.
I figured reusing Gustclan's name would probably be more helpful than making a third unrelated name to Burning Water, and I can't imagine horses choosing to live on Ltsooy-Tuu's land XD
It's not really much like Gustclan but bear with it ;3
I also thought referring to people as fleshy-feet was a good callback to the warrior clans.