Splendid Valley was originally the home of the majority of Equestria's Diamond Dogs.
Splendid Valley was rich in gemstones, making it a very appealing place for Diamond Dogs to live. The valley was located close to Old Olneigh.
During the War
The ponies of Old Olneigh mined Splendid Valley for gems. The local Diamond Dogs resisted the pony intrusion on their lands, before they were forcibly relocated by the military. When Splendid Valley had been completely mined of its gemstones, the Ministry of Arcane Sciences built the Maripony facility over Splendid Valley; resulting in heavy taint pollution.
Splendid Valley is populated by hellhounds and the area nearby is also populated by other creatures, like alicorns and floaters. Many holes, the entrances to hellhound tunnels, dot the landscape of the valley. There is also a huge crater from the megaspell that hit the valley during the Great War that glows faintly, even in daylight.
Most of the hellhound population in Spendid Valley was erradicated when Littlepip and her party detonated a balefire bomb megaspell in the hellhound tunnels directly below Maripony. This megaspell destroyed many of the tunnels and their inhabitants, and made the entire valley heavily irradiated.
- Incorrectly refered to as Pleasant Valley in Project Horizons, though this could very well be an alternate name for it.