Eyeing a little parcel in my town... but how to mitigate subsidence?

Hi all!

Haven't visited these forums in a while. I've found a little town in the province of Granada that suits me very well, and recently my thoughts turned (again) to building on a parcel.

Well, there's a little, inexpensive parcel right down the street from me. Sun exposure and view are ideal. Most of the space available is vertical, as you'll see in the attached pictures.

There is a huge, mysterious pile, seemingly of dirt, that occupies the middle of the lot. No worries if it is in fact dirt: it can be Bobcatted out of there. I will make sure that it IS dirt, and not rock, before I put any money down.

But... how did the dirt get there in the first place? Given what I see above the lot, I think it's due to rainwater runoff.

I do NOT plan to build a full-on multistory building: just a little casa de apero on the ground level and perhaps a platform for a yurt "living room" and a tent, at the height of the average story.

Oh, and I should also mention that this is a seismic zone. In my year here, I have yet to feel any tremors, but the designation is there for a reason.

How do I mitigate the subsidence risk?  I saw a suggestion for vetiver planting on the exposed hillside in this post, and that's a possibility depending on the upper bound of the lot on that hill.

If the house has a basement that pile may have come from digging the basement.

Otherwise, it just looks like it was dumped there for some unknown reason.

the bright color of the vegetation growing on it, compared to the surrounding that can be seen,  is of interest.

Heather Staas wrote:the bright color of the vegetation growing on it, compared to the surrounding that can be seen,  is of interest.

Good point. Any hypotheses?

I think in any event it's best for me to assume that There Will Be Erosion And Runoff.

Looking for mitigation strategies, although here in Spain I'll need to get signoff from a technical architect anyway if I want to build on the property, and that person should be able to suggest some methods.

I'm with you on the water run-off theory. It does look like an alluvial fan to me, as it's top is right by the low point of the clearly older and cut into original slope. That would explain the greener vegetation too, as it's where most of the run off water goes.
If you made the back wall of the house into a retaining wall, you could effectively have an earth berm house, but the fact that it looks like water deposited it, you could have 'water management issues'. That is a very steep slope above too. It's not a plot that appeals to me.