The murder case is 40 years old and has been a cold case for several decades, but authorities said they have new leads and hope to find the victim's body.
Notorious child killer Mack Edwards confessed to killing Madison and as many as 17 other children in the 50s and 60s.
Edwards killed himself while on death row in 1971.
Authorities said they did not have enough conclusive evidence to close this case and many others.
Investigators continued working the case on Monday, bringing out radar equipment and cadaver dogs.
"For a hit to be valid, the cadaver dogs have to work pretty much independently with their handler. They can't have too much information, and working all the different corners of this intersection of the 23 and Tierra Rejada. All of the cadaver dogs working independently hit on the same spot we're going to be digging today," said LAPD Lt. John Romero.
Edwards was a subcontractor that worked for Caltrans. He would reportedly murder the kids and take them to one of his work sites to bury the victims. Remains could be scattered across a number of California freeways.
Authorities said they have given themselves a 10-day window to keep the Tierra Rejada Road exit blocked.