The idea was to clean up graffiti, but a youth group in southwestern France got carried away and wiped out a bit of prehistory as well, damaging cave paintings thousands of years old.

French cultural officials are furious, and say they plan to file a complaint against the group.

"Absolutely stupid!" said Rene Gachet, director of cultural affairs for the Tarn-et-Garonne department, 400 miles southwest of Paris.

The head of the spelunkers club that arranged the youth group's cleanup blamed officials for failing to designate the site as a historic treasure and act to protect it.

The damage was done last Sunday, when about 70 members of the youth group descended on the Mayrieres cave near the village of Bruniquel, armed with steel brushes to clean up graffiti. They damaged a portion of the cave's 15,000-year-old bison paintings before realizing what they were.