In the book Indian in cupboard what does gash darned hallucy-nation mean?

In the book The Indian in the Cupboard, the phrase "gash darned hallucy-nation" is an expression of surprise and disbelief. It is an amalgamation of the words "gosh darned" and "hallucination". The phrase is used by Omri, the main character of the book, to express his disbelief at what he is seeing.