Interior Secretary Ryan Zinke's memo to President Donald Trump recommending that the president modify 10 national monuments created by his predecessors, including shrinking the boundaries of four, is fraught with factual errors and may be on shaky legal ground.

Any attempt by the administration to change the Cascade-Siskiyou National Monument is sure to trigger a legal challenge by monument supporters, and a lawsuit is already pending against the monument by timber interests.

We've known since August that Zinke was recommending reductions in the Cascade-Siskiyou monument, after The Washington Post quoted sources who had seen the recommendation. Now we have access to Zinke's written memorandum, again thanks to the Post, but it still doesn't say exactly how much of a reduction is being contemplated.

The document obtained by the Post is labeled "Draft Deliberative — Not for Distribution," indicating that it may be subject to change.

Some changes are in order.

For instance, the memo incorrectly says the original Cascade-Siskiyou declaration prohibited "motorized transportation." It also refers to the need to protect "hunting and fishing rights." Both hunting and fishing are allowed in the monument.

The memo gets into questionable legal speculation when it asserts that the 1906 Antiquities Act, which gave presidents the power to create monuments, was intended to protect “objects of historic or scientific interest,” and that biodiversity, for instance, is too broad a concept to be considered an "object." The Cascade-Siskyou monument was created — and expanded — to preserve the diversity of plant and animal species found there by protecting the area's unique habitats.

That sounds plausible, except that the U.S. Supreme Court ruled in 1920 that the entire Grand Canyon qualified as an "object."

In Cameron v. United States, the owner of a gold-mining claim challenged the government's order that he vacate and clean up his claim because it was inside the boundaries of the Grand Canyon National Monument (Congress later made it a National Park). Cameron argued the monument, more than 800,000 acres in size, violated the Antiquities Act requirement that a monument  be "confined to the smallest area" necessary to preserve the object in question.

The court unanimously disagreed.

"The defendants insist that the monument reserve should be disregarded on the ground that there was no authority for its creation," Justice Willis Van Devanter wrote. "To this we cannot assent. The act under which the President proceeded empowered him to establish reserves embracing 'objects of historic or scientific interest.' The Grand Canyon, as stated in his proclamation, 'is an object of unusual scientific interest.'"

So is the Cascade-Siskiyou bioregion.

Parts of the monument also are former Oregon & California Railroad lands, designated by Congress for sustainable timber production under the O&C Lands Act of 1937. Timber industry representatives and the O&C Counties Association say a presidential proclamation under the Antiquities Act cannot overrule an act of Congress.

The courts will rule on that question eventually. Meanwhile, monument supporters have vowed to challenge any changes ordered by the president on the grounds that he doesn't have the power to undo what his predecessors have done.

The courts, not Trump, will have the final say on the future of the Cascade-Siskiyou National Monument.