The four, aged between 16 and 25, were arrested after coming to the police's attention in the course of another inquiry and transferred to the prosecutors' office in Nîmes on Friday morning.
Two of them are minors, according to local paper Objectif Gard.
"They all more or less blame each other but have confessed to at least a part of the allegations," gendarmerie lieutenant-colonel Sébastien Bardoux told the AFP news agency.
Prosecutors are calling for all of them to be given prison sentences, according to regional paper Midi Libre.
A young man with a slight mental disorder was jailed for 18 months for arson in Nîmes on Tuesday.
Six months related to a suspended sentence from a previous conviciton for arson.
Thousands of hectares of scrub and forest have been ravaged by wildfires in the south of France and Corsica this summer.