To show contact (brown dotted line) between river-deposit-containing materails 
(F1)
to W and  deeply grooved materials (L) to E. One river deposit is highlighted
by red arrow.
River-deposit-containing materials overlie (white arrows) the deeply
grooved materials.
The deeply grooved materials rise steadily to the E (~1 degree slope)
to form the proto-Zephyria lobe.
River-channel-deposits within F1 are erosionally resistant and are locally
highstanding at the contact between F1 and L.

In this area, yardang-forming materials (topography above solid yellow lines) form
a relatively thin drape above the deeply grooved materials (L).
Crosscutting relatinships elsewhere prove that yardang-forming materials
postdate the river-deposit-containing materials as well.
We do not know the relative
Age of the mesas and knobs W of the contact (above thin dashed pink line). 
PEDR tracks (not shown) confirm the embayment relationship 
. Range of topography is from 
-2100 (red) to -2600m (white).