Tosten Walsh Lommen led officers on a 50-mile car chase in South Dakota.
When the 30-year-old eventually stopped, the officers said they found his mother’s body wrapped in a blanket in the back of his 4×4.
A post-mortem following the discovery on New Year’s Day found Michelle Walsh, 58, died from head and neck injuries.
Lommen has been charged with murder in California after authorities accused him of killing Ms Walsh at their home in Palm Springs.
However, on Friday he refused to be extradited from Rapid City, South Dakota, to face the charge, police said.
Charges of felony aggravated eluding and misdemeanour drunk-driving, reckless driving and resisting arrest were dropped by South Dakota’s assistant attorney general so Lommen could face the more serious charge.
“We dismissed our file so Lommen could go back to California,” attorney general spokeswoman Sara Rabern told the Capital Journal.
“The much more serious charges he is facing are out west.”
Lommen remains in custody in Rapid City with a $2.5m (£1.8m) bail.