What is this world: mountain, river, or mirage?

When one arrives at the mountain
one finds a fixed collection of matter.
Sure, it’s slowly changing its arrangement,
bits of grit erode off,
cracks develop, splitting rock from boulder,
but the long-and-short of it is that it’s a bunch of stuff.

When one arrives at the river one finds it exists
but is never the same arrangement of stuff.
With the pass of a second of time,
it’s completely rearranged itself.

If one could ever reach the slyly retreating mirage,
one would find that it was purely an illusion —
or, more precisely, you’d never find it because it’s not there.

Maybe it’s all three combined in some way
that my mind can’t comprehend.

Maybe it’s none of the above —
and, instead, is something outside my capacity to imagine.

Yes. That’s probably it.