So my take-a-way is your total 18 mile trip took roughly 40% of your battery which would mean on a full battery you would have had a 45 mile range, IMO not too bad considering the elevation change. I'd like to see any ICE vehicle suffer an only ~35% MPG reduction for such a change in elevation.
On your way back(downhill) were you forced to use your friction brakes much? or was B or ECO mode enough to slow down your decent enough to keep from crashing? Sure regen isn't as efficient as coasting but it's sure a hell of a lot better than brakes or even ICE engine breaking.
I've also noticed with our old Prius and it's tiny battery that hills seem to affect it much less than a straight ICE vehicle where hills can really kill MPG.
2012 SL purchased used 2/'16
2013 S w/QC purchased new
Juicebox Premium 60a L1/L2 EVSE, Ebusbar 16a L1/L2 EVSE
'12 EVSEupgrade'd 20a L1/L2 EVSE, '13 EVSEupgrade'd adjustable 6-20a L2, 6-13a L1 EVSE
Zencar 13, 20, 30a L1/L2 portable EVSE
GE Durastation 30a