I just loaded up my save on an oasis biome and the cold springs had turned to sand. I noticed that it was raining so perhaps it was this bug. The season is currently summer, colony is only one season old. I'm running the Star Wars mods and a bunch of other litlle ones, but none of them mess with weather or terrain. Out of all the error messages this one seemed to be the most relevent.

Could not load reference to Verse.TerrainDef named TKKN_ColdSprings
Verse.Log:Error(String)
Verse.ScribeExtractor:DefFromNode(XmlNode)
Verse.Scribe_Defs:Look(TerrainDef&, String)
TKKN_NPS.cellData:ExposeData()
Verse.ScribeExtractor:SaveableFromNode(XmlNode, Object[])
Verse.Scribe_Collections:Look(List`1&, Boolean, String, LookMode, Object[])
Verse.Scribe_Collections:Look(List`1&, String, LookMode, Object[])
Verse.Scribe_Collections:Look(Dictionary`2&, String, LookMode, LookMode, List`1&, List`1&)
Verse.Scribe_Collections:Look(Dictionary`2&, String, LookMode, LookMode)
TKKN_NPS.Watcher:ExposeData()
Verse.ScribeExtractor:SaveableFromNode(XmlNode, Object[])
Verse.Scribe_Collections:Look(List`1&, Boolean, String, LookMode, Object[])
Verse.Scribe_Collections:Look(List`1&, String, LookMode, Object[])
Verse.Map:ExposeComponents()
Verse.Map:ExposeData()
Verse.ScribeExtractor:SaveableFromNode(XmlNode, Object[])
Verse.Scribe_Collections:Look(List`1&, Boolean, String, LookMode, Object[])
Verse.Scribe_Collections:Look(List`1&, String, LookMode, Object[])
Verse.Game:LoadGame()
Verse.SavedGameLoader:LoadGameFromSaveFile(String)
Verse.Root_Play:<Start>m__0()
Verse.LongEventHandler:RunEventFromAnotherThread(Action)
Verse.LongEventHandler:<UpdateCurrentAsynchronousEvent>m__1()

Still happening for me.
In a desert biome, perpetual summer, new game.
I'm using a few other mods but I dont think anything that messes with maps, except configurable maps and map generator.

Playing on Redwood Forest, in Summer, Rainy Thunderstorm happened. After it had ended, and the ground started to dry out, huge portions of the map started turning into sand.

Mods installed:
Hugs Lib
Simple Sidearms
Repair Workbench
Facial Stuff 0.18.0
While You're Up
Stack Merger
[B-18]-LinkableDoors
Nature's Pretty Sweet
More Furniture [B18]