But isn't that Hammada? You say Hah-mah-dah, I say Hay-may-dah, let's call the whole thing off ...
Hammada isn’t an
alluvial fan nor a
bajada.
Hammada is typically a fairly flat surface and is composed mostly of rocks because most all the sand has been removed by wind. It is therefore a result of aeolian erosion (i.e. wind took away stuff). In ASL it provides no TEM and doesn’t bog because it is in fact a fairly flat surface with good traction, rather it immobilizes because of damage to tires and potentially prolonged abuse of the suspension and axles (see footnote in the RB).
Alluvial fans and bajada are conversely the result of alluvial deposition (i.e. water added stuff). They are not at all flat, instead being crossed by numerous shallow braided washes and could provide TEM. They most definitely could bog. One could model the present main channel near the top of an alluvial fan as a wadi, but the rest of the fan or bajada might be well represented by broken ground.
The description of the broken terrain transformation doesn’t really sound like it is modeling alluvial fans though. It sounds a bit more like modeling well eroded
Hoodoo terrain. The crag transformation being the hoodoo like pinnacles which are then surrounded by broken ground representing the debris and alluvium from the easily eroded deposits protected by the cap layer that formed the pinnacles/hoodoos. These are sort of like mini alluvial fan areas in formation on a much smaller scale. Again, good for some TEM and potential for bog.
But honestly I don’t know what it is meant to model as I didn‘t write the rules! Maybe look up the locations of scenarios that use Broken Terrain and see what their geology is?