Piece of some Yosemite monument (4)
I believe the answer is:
item
'piece' is the definition.
(I've seen this before)
'some yosemite monument' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'ITEM' can be found hidden inside 'yosemite monument'.
'of' is the link.
(Other definitions for item that I've seen before include "Record" , "Article (on list or in news)" , "Two people considered together (informal)" , "Seperate article in an enumeration" , "Whole individual unit" .)