Get Y value of plane at position X,Z

I’m trying to do a jump, and I just need to basically detect when the player is back on the ground, and I’ve already got it all sorted out, I just need to know if it’s possible to get the Y value of a X,Z position on a plane. To back up my terrible explanation, here’s a diagram, which is equally terrible.

34360-untitled.png

A pseudo way of putting what I’m after would be Y = the Y value of the plane at position X,Z

You can Raycast in downward direction from that point. And use RaycastHit.point to get y value.