Out of sight
Of course, the expression 'out of sight' has a literal meaning, that is, 'beyond the range of sight' and will have been used that way for as long as the language has existed.
However, 'out of sight' as a metaphorical phrase is commonly thought of as language of the hippie period, and it was so prevalent then as to have been abbreviated to 'outasight'. The derivation of that era's use of the phrase was an extension of another hippie expression - 'far out'. Some people or things were so far out they were 'out of sight'. Whatever mind-altering substances the person who coined it might have been influenced by the existing phrase 'out of sight, out of mind' may also have been an influence.
Despite that strong association with California and flower power, both 'out of sight' and 'far out' were coined in the more restrained Victorian period. At least the country of source is correct, as these early US citations show:
J. Fraser's 1891 novel Train Wreckers - "Now if Daisy would only put in an appearance this would be an out of sight chance to pop the question."
S. Crane's 1893 novella Maggie - "You're the kind of a man we like, Pete. You're outa sight!"