A slope that’s slippery in US city (2,4)
I believe the answer is:
el paso
'us city' is the definition.
(city in Texas)
'a slope that's slippery in' is the wordplay.
'that's slippery' is an anagram indicator (I've seen this in other clues).
'in' indicates putting letters inside.
'slope' anagrammed gives 'elpso'.
'a' placed into 'elpso' is 'EL PASO'.
(Other definitions for el paso that I've seen before include "US city" , "Texan city" , "West Texas town" , "City of Texas on the Rio Grande; aslope (anag.)" , "city on Mexican border" .)