Washington (CNN) On May 16, 2017, Interior Secretary Ryan Zinke met with Rep. Chris Collins, a New York Republican who was the first in Congress to endorse Donald Trump's presidential candidacy, according to Zinke's official calendar.

But Zinke's calendar doesn't show who else was in the room -- three representatives from a company that does business with the National Park Service.

The meeting is one of about a dozen instances uncovered by CNN of Zinke's calendar omitting or obscuring important details, leaving the public in the dark about who is meeting with Zinke, one of Trump's most trusted cabinet officials with a consequential portfolio.

The situation is compounded because the Interior Department hasn't distributed Zinke's upcoming schedule in nearly a year. It only releases his calendar when a Freedom of Information Act request is made. About a year's worth of his schedule has been released, yet those calendars are not a complete record of the secretary's activities. And even the calendars that have been released due to public records requests are currently five months old.

Zinke met with three executives of Delaware North, a contractor that runs hotels, restaurants and shops in several national parks, including in Grand Canyon and Yellowstone. Delaware North also runs a hotel in Zinke's hometown of Whitefish, Montana, located about 20 minutes outside of Glacier National Park.

A briefing memo for the secretary painted a picture of the meeting as focused not on Collins, but Delaware North. "This is just an overview from Delaware North regarding how NPS works with concessionaires," reads the memo, released through a Freedom of Information Act request.

The only mention in the memo of Collins -- who represents an area of New York near the Delaware North corporate headquarters -- is a note that he and his chief of staff would be in attendance. Collins' office and Delaware North did not respond to requests for comment on the meeting.

CNN and the Center for Western Priorities, a nonpartisan conservation group that opposes Zinke's policy initiatives, separately reviewed Zinke's calendars and compared them to email conversations between Zinke and his scheduling aide, all of which were released over the past few months under the Freedom of Information Act to groups seeking greater transparency.

The analyses found several examples the secretary's calendar not including a full list of attendees or agenda items. In some cases, names are redacted. In others, aides note some of the meeting attendees but not all, or use non-descript terms like "personal" and "hold," including when Zinke met with a federal contractor.

A similar investigation looking at former EPA Administrator Scott Pruitt's calendars led to CNN uncovering a "secret" calendar maintained by Pruitt's aides. A former Pruitt deputy chief of staff said aides met regularly to "scrub" potentially controversial meetings from his calendar. Pruitt resigned days later, under a cloud of ethics questions.

There are no allegations of a similar effort to scrub calendars in Zinke's department, but unlike Pruitt, Zinke does not produce a regularly updated calendar nor provide the beat reporters covering his department regular updates on his upcoming events.

"He shows the same deliberate lack of transparency that brought down Scott Pruitt," said Rep. Raul Grijalva, the top Democrat on the House Natural Resources Committee, of Zinke. "If he won't stop having suspect meetings on taxpayers' time, the least he could do is release timely, accurate information about how he spends his days as a public servant."

Zinke's whereabouts are not readily available to the public. The last posting about an upcoming event on the department's website is dated nearly a year ago, on July 27, 2017. Almost nine months have passed since the last update to "On the Road with Secretary Zinke," a blog -- occasionally written in first person -- about Zinke's visits to national parks and other department facilities.

In a statement, Interior spokeswoman Heather Swift said Interior "complies with all applicable laws, rules, and regulations."

"We always strive towards transparency which is why we include additional information in briefings that are made available to the public," Swift said. "Additionally, it's very common for schedule items to be canceled the day of, which is why something could be referred to in an email or briefing and not be on the calendar released."

But Swift also acknowledged the agency hasn't posted notices on Zinke's upcoming events to its site in nearly a year. She said the agency decided to only e-mail notices directly to local news outlets when Zinke travels to their areas. "We send one to local press every time the Secretary travels if there's open press (opportunities)," Swift said.

Similar to what CNN found when examining Pruitt's calendar, there are cases, such as the Delaware North meeting, where Zinke's calendar revealed some but not all of the meeting attendees.

A May 31, 2017 meeting in Alaska, for example, is noted on Zinke's trip itinerary as "Meeting with Mayor Harry Brower, North Slope Borough." But a briefing packet prepared ahead of the trip notes that two lobbyists from Van Ness Feldman, a firm that represents the borough in a lawsuit against the Interior Department, were also present.

In other cases, events were included on Zinke's calendar, but redacted before the documents were made public. The redaction note "NR," or non-responsive, does not disclose why the redaction was made, and in multiple instances, the redacted information involves agency business. Swift said the department's solicitor's office handles redactions.

That type of redaction was made of Zinke's May 18, 2017 visit to an Interior-owned gun range with the US Park Police, an arm of the Interior Department. The visit is redacted from his calendar without an explanation for why, but CNN found references in two emails from his scheduling aide, including as "Shooting Range Day with Park Police."

Zinke has previously come under scrutiny for questionable uses of Park Police resources: He has used their helicopters to attend events, and brought a Park Police security detail on his family vacation to Greece and Turkey last year.

Redactions occasionally mask seemingly innocuous information, such as when Zinke ate dinner with a former Trump transition official on May 24, 2017 or when he attended an event described as Navy "SEAL Night" the day before. Zinke is a former Navy Seal.

Interior officials also redacted Zinke's meeting with the grandson of a congressman on the topic of "college football" on June 9, 2017. The congressman, Republican Rep. Jack Bergman of Michigan, sits on the committee overseeing Zinke's department. Zinke played college football at the University of Oregon. The congressman's office did not respond to a request for further information on the meeting.

Swift described it as a mentoring session. "This was a personal meeting with a young man who was considering playing football in college," Swift wrote. She says it was redacted because it was personal and not department business.

Certain entries are described in vague ways, such as "personal" or "hold." The Center for Western Priorities found a case where generic words shielded from public view the name of a government contractor who met with Zinke last September.

Grijalva says he plans to ask for an investigation.

"The kind of entitlement sense that they brought into their positions -- like I'm not going to worry about these little ethics issues," he told CNN. "What's that? That doesn't apply to me. Hell with them, they shouldn't get the calendar. And I can meet whoever I want and nobody needs to know about it."

CORRECTION: This story has been updated to correct the date on which Zinke met with Rep. Chris Collins.