No , really anywhere in the Americas you can ride officially with your oficial California USA drivers license, or any other state's or province's .
The IDP is only a formula document translating the data from your state license into a cluster of languages, it has no value without your actual license as backup with it, i.e. if you loose your driving priveleges for some reason the IDP is also invalidated.
Just because some cops look for la mordida is no guarantee that they will fall to the ground crying in fear and awe as you whip out your IDP
If it comforts you to spend $15 or $20 to get the IDP then do so.If you want to create fake documents go whole hog,make an official passe partout signed by the viceroy of New Spain , King Juan Carlos and Simon Bolivar.
The only thing you should really copy is your actual drivers license, laminate it ,whatever,multiple copies. Then if some ne'er do well cop starts at you , proffer the copy.Comes in handy too in your daily need to show ID without having to get out the real item.
The US and Canada are not the only ones to make driver's licenses in credit card format. A very good idea, better than the European system of having big fold out documents, with sub sections, loose parts etc etc The newer ones have all the hi-tech features, magnetic strip,hi-def pictures , maybe soon microchip.And that goes for some of the Latin american countries too. Soon they will all have the scanners and card readers at the ready. Oops , better show the real one if the cop has all the equipment at the ready

(spelling correction)

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http://advrider.com/index.php?thread....207964/page-5 then scroll down to post #93