Dealing a crushing combination to the Pac-12 on Friday, the Big Ten announced Oregon and Washington would be joining the conference next August, and the Big 12 completed its raid of the beleaguered league by adding Arizona, Arizona State and Utah.

The day began with hope and nine members for the Pac-12. It ended with the Pac-12 — with roots that date back a century and more NCAA championships than any other — down to four schools and facing extinction because it was unable to land a media rights agreement to match its competitors.

“Today’s news is incredibly disappointing for student-athletes, fans, alumni and staff of the Pac-12 who cherish the over 100-year history, tradition and rivalries of the Conference of Champions,” the conference said in a statement. “We remain focused on securing the best possible future for each of our member universities.”

The super-conference era has arrived in college sports, and it has swallowed the Pac-12 — the conference that produced Jackie Robinson, John Elway, Jackie Joyner-Kersee and Barry Bonds.

After the Big Ten paved the way Friday morning for the Pacific Northwest rivals to join, the Ducks were first to make it official with a unanimous vote by the school’s 13 trustees. The Big Ten a short time later said its presidents’ council had voted to accept Oregon along with Washington and become an 18-team coast-to-coast conference, with four West Coast members.

UCLA and Southern California announced last year that they would leave the Pac-12 for the Big Ten in 2024.

“Our student-athletes will participate at the highest level of collegiate athletic competition, and our alumni, friends, and fans will be able to carry the spirit of Oregon across the country,” Oregon President John Karl Scholz said.

The Big 12, meanwhile, had three more Pac-12 schools in its sights, a week after luring away Colorado.

Arizona’s entry was approved Thursday night, but the Big 12’s long-brewing expansion plan was far from complete.

Once it became apparent on Friday that Oregon and Washington were leaving the Pac-12, Arizona State and Utah didn’t have much choice but to jump, too. The Big 12 presidents OK’d the Sun Devils and Utes, and soon after the conference made it official. The Big 12 will be a 16-team conference, spanning from Florida to Arizona, in the fall of 2024.

“We are thrilled to welcome Arizona, Arizona State and Utah to the Big 12,” said Commissioner Brett Yormark, whose aggressive approach in his first year on the job has sent shock waves across major college sports. “The Conference is gaining three premier institutions both academically and athletically, and the entire Big 12 looks forward to working alongside their presidents, athletic directors, student-athletes and administrators.”

Beyond this school year, the Pac-12 is down to the Pac-4 — Stanford, California, Oregon State and Washington State.

The Big Ten’s latest grab from its Rose Bowl partners comes a little more than a year after it landed Southern California and UCLA. The Big Ten will be the largest conference in major college sports, spanning 15 states from New Jersey to Washington.

“The Big Ten is a thriving conference with strong athletic and academic traditions, and we are excited and confident about competing at the highest level on a national stage,” Washington President Ana Mari Cauce said.

Pac-12 leaders met early Friday to determine if its remaining schools would accept the potential media rights deal with Apple that Commissioner George Kliavkoff presented this week.

Two people with knowledge of the discussion between the Big Ten and Oregon said the Ducks were leaning toward staying in the Pac-12 late Thursday, boosting the possibility that others would stay put, too.

Instead, Oregon officials notified the Pac-12 early Friday they were still uncomfortable with the Apple deal and the school would be re-engaging with the Big Ten.

“We are disappointed with the recent decisions by some of our Pac-12 peers,” Washington State President Kirk Schulz and athletic director Pat Chun said Friday before its Apple Cup rival announced it was leaving, “While we had hoped that our membership would remain together, this outcome was always a possibility, and we have been working diligently to determine what is next for Washington State athletics. We’ve prepared for numerous scenarios, including our current situation.”

Former Big Ten Commissioner Kevin Warren had encouraged member schools to consider adding Oregon and Washington after the conference landed the two Los Angeles schools last summer, the blow that began the Pac-12’s descent.

Less than two weeks ago, Big Ten Commissioner Tony Petitti said his presidents and chancellors wanted him to focus on USC and UCLA’s transition to the Big Ten and not more expansion. Now, the Pac-12’s two biggest remaining brands and perennial football powers are heading for a new home. Their closest conference neighbor, the University of Nebraska, will be more than a 1,600-mile drive away.

Oregon and Washington will receive a reduced payout, Scholz confirmed, compared to current Big Ten members and to USC and UCLA, which are projected to receive more than $60 million each in media rights revenue from the league starting next year. A person familiar with the negotiations said the Ducks and Huskies would receive about $30 million per year for its first six years in the conference, with annual escalators and the ability to draw on future payments.

Washington and Oregon were charter members of the Pacific Coast Conference in 1916, the organization that eventually became the Pac-8, then 10, then 12.