Vince Mayle caught two TD passes and Teondray Caldwell, Jeremiah Laufasa and Marcus Mason also scored touchdowns for the Cougars (4-2, 2-1 Pac-12), who last beat the Golden Bears (1-4, 0-2) in 2002.
Freshman Jared Goff threw for 489 yards and two touchdowns for his third 400-yard passing game already this season and Chris Harper had 13 catches for 216 yards and a score. But it wasn't enough to give coach Sonny Dykes his first win against an FBS opponent in a disappointing debut season with the Bears.
Cal's only win this season is against lower-division Portland State and the Bears current nine-game losing streak to FBS opponents since beating Washington State Oct. 13, 2012, is the longest of any team in a BCS conference.
Halliday and Goff both bounced back from rough outings a week ago against conference powerhouses. Halliday was knocked out of the Cougars' loss to No. 5 Stanford last week and Goff was pulled after losing a pair of fumbles in the opening quarter during a torrential rain storm in a 55-16 loss at No. 2 Oregon.
They traded big plays on an afternoon as they combined for 1,010 yards passing against overmatched defenses.
Halliday's 72-yard TD pass to Mayle gave the Cougars a 35-15 lead late in the third quarter after Cal was stopped on a fourth-and-1.
But Goff answered right back with a 53-yarder to James Grisom to get the Bears within 13. But Cal couldn't get any closer as Washington State got its most lopsided conference win since beating UCLA by 22 in 2006. The Cougars had their highest-scoring conference game since beating Oregon 55-16 in 2003.
The game marked a reunion for the coaches. Dykes spent seven years as an assistant under Washington State coach Mike Leach at Texas Tech and credits his mentor for teaching him the nuances of the spread offense he currently uses at Cal.
A game featuring Leach's "Air Raid" offense against Dykes' "Bear Raid" version got off to a predictable start with the teams throwing for 622 yards in the first half as the Cougars took a 21-15 lead into the break.
There could have been even more scoring except lost a pair of fumbles by Daniel Lasco and Brendan Bigelow after driving inside the Washington State 10 with Kalafitoni Pole recovering both of them.
Cal had better luck reaching the end zone from inside its own 20 than near Washington State's goal as Goff found Harper behind the coverage for an 89-yard score in the second quarter for the second longest pass play in school history. Zach Maynard and Keenan Allen have the record with a 90-yard TD pass two years ago against Washington.
The Cougars answered with a 68-yard TD pass from Halliday to Mason, who took a swing pass and cut back through the Bears defense for the long score to make it 21-12.
Cal began the day by announcing that starting center Chris Adcock was out for the year with a knee injury and safety Alex Logan retired for medical reasons. Then the Bears lost cornerback Stefan McClure (knee) and linebacker Jalen Jefferson (head) in the first half and cornerback Joel Willis was taken off on a stretcher after the opening kick to the second half.