The most common and most likely answer to this crossword clue is the 12 letter word INTERCOASTAL
I've seen this crossword clue in The Guardian
I
N
T
E
R
C
O
A
S
T
A
L
Buddy explains!
The straight part
We know that "between New York and California, perhaps /between New York and California, perhaps" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case between new york and california, perhaps /between new york and california, perhaps = intercoastal.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.