I eye Tom’s contraption in a Californian National Park (8)
I believe the answer is:
yosemite
'a californian national park' is the definition.
(I've seen this before)
'i eye tom's contraption' is the wordplay.
'contraption' indicates an anagram.
'i'+'eye'+'toms'='ieyetoms'
'ieyetoms' with letters rearranged gives 'YOSEMITE'.
'in' is the link.
(Other definitions for yosemite that I've seen before include "Natl. Park in California" , "California falls, valley, park" , "US National Park in California" , "Area of beauty" , "Where there are watery cascades" .)