Yes this is right, but it shows only item of "(cdr (assoc pop poplist)" , it must show items of each list like "alist"
(setq alist '("Orchard" "Wall" "Pool" "Building"))
(setq plist '("region1" "region2" "region3"))
(setq slist '("riverNG" "riverTH" "riverCR"))
popup1 > alist
popup2,popup3 > plist
popup3 > slist