If it is above the passenger rear wheel and the trunk is not wet, then the coolant most likely came out of the coolant overflow.
This happened to me and the entire coolant tank drained out. After a trip to the dealer and $600 later it turned out to be nothing. Basically, they told me an air bubble or something can just cause the coolant to come out of the overflow and it really does not mean anything is wrong with the car.
Hope this helps!
Porscha
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