Hot rock in Los Angeles and Virginia (4)
I believe the answer is:
lava
'hot rock' is the definition.
(I've seen this in another clue)
'los angeles and virginia' is the wordplay.
'los angeles' becomes 'LA' (abbreviation).
'and' means one lot of letters go next to another.
'virginia' becomes 'va' (US state abbreviation).
'la'+'va'='LAVA'
'in' acts as a link.
(Other definitions for lava that I've seen before include "Volcanic spillage" , "Unstoppable red tide" , "Stuff heatedly hurled out" , "Hot flowing rock" , "Molten rock expelled by a volcano" .)