The Guanajuato mummies were discovered in a cemetery of a city named Guanajuato northwest of Mexico City (near Léon). They are accidental modern mummies and were literally "dug up" between the years 1896 and 1958 when a local law required relatives to pay a kind of grave tax.* You could pay the tax once (170 pesos) and be done with it; this option may have appealed to wealthier individuals. But you were also allowed to pay a yearly fee (20 pesos); this would have appealed to less wealthy families. However, if the relatives could not pay this yearly tax for three years, the body (which had, by the way, become accidentally mummified) was dug up from the cemetery and (if the fee still wasn't paid) placed on display in El museo de las momias. [Of course, what if the person's family had moved from town--or what if the person was the last person from their family? Well, it didn't matter; the law was the law!]
Fortunately, in 1958, the law was changed. Although no new bodies have been exhumed, the museum still displays the original mummies.

According to an article in the Arizona Republic (November 1, 2005), the mummies began attracting tourists in the early 1900s, "when cemetery workers began charging people a few pesos to enter the ossuary building where bones and mummies were stored. But business really took off after the 1970 movie Santo Versus the Mummies of Guanajuato, starring masked wrestler Rodolfo Guzmán Huerta."

indicates that the first mummy was found in 1865 and that the museum opened in 1894

A combination of the soil conditions and a dry climate of the mountainous area caused the bodies in the local cemetery to dry out naturally before they could decompose. The bodies were placed in tombs, seven rows high; apparently, those in the middle row were more likely to have been naturally mummified. However, only those who failed to pay the grave tax were ever exhumed so information about mummification will always be incomplete.

The Guanajuato mummies are some of the strangest ones ever placed on display. Some are clothed, some aren't. A few are wearing only their socks and/or shoes. Some are old, others are only infants. One tiny baby mummy is labeled, "La momia más pequeño del mundo"--the smallest mummy in the world. The baby and the mother (they died during a caesarean section) are in the museum, but they will not be found together.
The museum contains a few local legends as well. For example, one body was said to belong to a woman who had been buried alive. When the Mummy Road Show hosts researched the mummy, they concluded that two factors suggested this legend was correct: the woman's arms were raised over her face and her forehead had scratch marks.