WASHINGTON — Supreme Court Justice Antonin Scalia’s head was under a pillow when he was found dead at a Texas ranch, according to the ranch owner who found his body.

“We discovered the judge in bed, a pillow over his head. His bedclothes were unwrinkled,” Texas millionaire John Poindexter told the San Antonio Express-News Sunday, describing how he found the 79-year-old jurist in the “El Presidente” suite at Poindexter’s 30,000-acre luxury ranch on Saturday.

“It looked like he had not quite awakened from a nap,” Poindexter said.

He later told the New York Times, “His hands were sort of almost folded on top of the sheets. The sheets weren’t rumpled up at all.”

While some reports claimed Scalia’s death was caused by a heart attack, Presidio County Judge Cinderela Guevara said he died of “natural causes.”

Guevara told the Associated Press that Scalia’s personal physician, as well as sheriff’s investigators, said there were no signs of foul play.

There was no autopsy at the family’s request and his body was flown from El Paso to Washington, DC, late Sunday afternoon.

Scalia was described as “animated and engaged” during a dinner on Friday night.

“He was seated near me and I had a chance to observe him,” Poindexter said. “He was very entertaining. But about 9 p.m. he said, ‘It’s been a long day and a long week. I want to get some sleep.’ ”

Meanwhile, Sen. Ted Cruz pledged on Sunday to filibuster any Supreme Court nominee put forth by President Obama to fill the seat of the late justice — claiming the November election should be a “referendum” on the court’s direction.

“This should be a decision for the people,” Cruz told ABC’s “This Week.” “We’ve got an election.”

Scalia’s sudden death sent shock waves through official Washington, as the replacement for the conservative justice could reset the political leaning of the Supreme Court for a generation.

But Republicans such as Cruz intend to keep the court one justice short until after the election, hoping that a GOP win in November would mean Scalia is replaced by a justice who shares his conservative views. Republican Senate Majority Leader Mitch McConnell also called for the vote on a replacement to wait.

Democrats, however, mocked the GOP, saying Republicans were playing politics with a constitutional presidential power.

“Ted Cruz holds the Constitution, you know, when he walks through the halls of Congress,” Sen. Charles Schumer mocked on “This Week.” “Let him show me the clause that says the president is only president for three years.”

Scalia’s loss will be felt as the Supreme Court takes up hot-button issues this session, including Obama’s immigration action, abortion, affirmative action in college admissions, voting rights and public-sector unions.

Many of the cases were expected to be 5-4 decisions, with Scalia in the conservative majority.

Supreme Court watchers suggest Obama choose a mainstream jurist who could make history for adding diversity to the court while making it hard for Republicans to refuse.

But given the already tense environment, one legal scholar suggests the president bypass the Senate.

“It may make sense for the president to take advantage of this recess and appoint a Supreme Court justice to serve out the remainder of the congressional term,” said Adam Winkler, professor at the UCLA School of Law.

The White House said Obama will make his nomination “in due time.”