How to Make Classic Cocktails, According to the U.S. Government

— -- Archive this under awesome American history. An engineer for the United States Department of Agriculture Forest Service Region 8 created a detailed “Cocktail Construction” chart in 1974, essentially making the government’s first and only cocktail cookbook.

The drawing, signed “Ketcham,” is believed to be made by civil engineer Cleve Ketcham, who died in 2005. It was found by the National Archives rolled up in a tube with 20 maps and drawings and intricately shows how to make whiskey sours, martinis, manhattans and more.

“Around the office we call these sorts of things history mysteries," Forest History Society historian James Lewis told ABC News. “You have to wonder if he wasn’t creating it for some sort of office party. Things were a little more like ‘Mad Men’ than they are today.”

The chart has a legend for different designs depicting grenadine, bourbon, lemon juice, scotch, cola and more. Serious attention is paid to the measurements of each ingredient.

“The drawings are very meticulous, very precise, very much the work of an engineer. This was not done lightly or quickly,” Lewis said. “The level of detail is very impressive and something like that in construction drawings for a bridge or something like that.”

Lewis has reached out to Ketcham’s son to see if the signature or handwriting matches that of his father. The chart says the recipes are by “SS&M, self-appointed barmasters” and were checked by “I Mixum,” “I.P. Freely” and “Jim Beam,” proving that the engineers were really having fun with this one.

“I think it’s fun that all these years later it’s getting attention,” Lewis said. “It shows that the Forest Service employees take their job seriously, but they are not always deadly serious about the job they do.”