(CNN) Ryan Zinke's very first meeting as interior secretary was never put on his official calendar.

It was a meeting scheduled to last five minutes with Chris Cox , the executive director of the National Rifle Association's lobbying arm, on the sidelines of an event with other sportsmen.

Then on his second day in office, Zinke was scheduled to meet with Karl Simich, an apparent reference to the managing director of Sandfire Resources , an Australian mining company that had been trying to develop a copper mine in Central Montana for at least six years. It also wasn't listed on hiscalendar.

The meetings are coming to light now only because of internal memos and other notes, released through a Freedom of Information Act request, that reveal these meetings and others that were not noted on his calendar, glaring omissions from what is supposed to be a complete record of the secretary's activities.

The monthly calendars the Interior Department has released publicly in response to Freedom of Information Act requests have often left off or obscured some meetings. More detailed accounts of Zinke's time are found in separate briefing memos prepared by his staff, which have not been released with the calendars and were obtained only by filing another FOIA request.

calendar between his first day in office in At least six more meetings were omitted from Zinke'scalendar between his first day in office in March 2017 and July of that year, Western Values Project discovered. The findings of the public lands advocacy group, which has been critical of Zinke, were corroborated by CNN.

Chris Saeger, the executive director of the Western Values Project, said Zinke is "keeping the public in the dark about meetings with the same corrupt special interests that brought this administration to power."

Keeping meetings off official calendars goes against the usual practice of a Cabinet secretary and flies in the face of transparency practices, according to experts who have talked to CNN.

"If I was your boss -- and the American people are the bosses -- I would love to know what you're doing with your time," said Elizabeth Hempowicz of the Project on Government Oversight, a nonpartisan advocate for open government. The incomplete release of calendar information "removes the ability of the public to do any oversight," such as seeing with whom public servants are meeting.

It raises the question, Hempowicz said, "What are you trying to hide?"

The Interior Department declined to comment on specific omissions or redactions from Zinke's calendar, referring instead to the statement it issued when CNN reported in September on vague language used to describe events on Zinke's calendar.

"We work to ensure the accuracy of the secretary's calendar, which is constantly changing, and will continue to be transparent in our scheduling process," spokeswoman Heather Swift said in a written statement at the time. "The secretary has one calendar which is submitted to the FOIA office where it goes through standard processing by career officials to ensure full compliance with all laws, rules and regulations. For most meetings, there is a memo which provides more context. These memos are available and regularly released to the public and media via the standard FOIA request."

omitted meetings or details of meetings. For example, his calendar described a meeting in May 2017 as between Rep. Chris Collins, a New York Republican, and him, but a memo prepared for the secretary ahead of the meeting revealed that executives from a large hospitality company that does business with the Interior Department also were there. Zinke's calendar has been under scrutiny since a CNN report in July first exposed that itomitted meetings or details of meetings. For example, his calendar described a meeting in May 2017 as between Rep. Chris Collins, a New York Republican, and him, but a memo prepared for the secretary ahead of the meeting revealed that executives from a large hospitality company that does business with the Interior Department also were there.

After that report, Zinke's office began publishing each week an unofficial outline of his schedule for the preceding week on the Interior Department website. The official calendars and the briefing memos for that time have not yet been released, however.

Separately, it released two months of his calendars , May and June 2018, in response to a FOIA request but those calendars lacked key details more so than the monthly calendars his office had released previously. Instead of noting topics or attendees, many entries were recorded only as "external meeting" or "internal meeting," meaning it was impossible to tell what the secretary was doing or with whom he was meeting.

Missing calendar items played a role in the downfall of another Trump appointee, former EPA Administrator Scott Pruitt, who resigned in July after a myriad of scandals culminated with a CNN report that he kept a secret calendar showing meetings with industry that had been omitted from his public schedule.

"Much like the ousted EPA Administrator Scott Pruitt, Zinke has been keeping a secret calendar that includes everything from meetings with lobbyists and coal executives to oil and gas CEOs," Saeger, of the Western Values Project, said in his statement. "How many more secret meetings that could be undermining our American birthright -- public lands, public access and national parks -- are being withheld from the public by Zinke and his office?"

Undisclosed meetings with energy industry

Among the new Zinke records are emails and briefing documents from his scheduler with subject lines like "Secretary Daily Schedule." The documents list time frames, locations and attendees for meetings that do not appear on the calendar Zinke's office released.

Norm Eisen, the Obama administration's co-called ethics czar, said the omissions are outside the norm and show "a shocking pattern of affirmatively concealing meetings with special interest influencers."

"It appears to violate federal law, which in my view requires that such records be maintained and produced," said Eisen, who is board chairman of the nonprofit Citizens for Responsibility and Ethics in Washington, a senior fellow at the Brookings Institution think tank and a CNN political commentator.

Several of the undisclosed or obscured meetings included representatives from energy companies, whose interest in the Interior Department could stem from its ownership of public lands, regulation of mining and some energy production, and enforcement of certain environmental laws.

For example, although Zinke was scheduled to meet on two occasions in 2017 with representatives of a major coal company, Peabody Energy, neither encounter is accurately described on his calendar.

In May, Zinke was to meet for dinner at the Trump-owned hotel in Washington with Scott Mason , an apparent reference to the former Trump campaign official who's now a Peabody lobbyist. Zinke's calendar indicates an event at that time, but the topic and attendees are redacted.

That June, three Peabody executives were scheduled to meet with Zinke, according to emails from his scheduler. The secretary's calendar disclosed only "Peabody Energy" -- with no way to tell whether that was the topic of the meeting or a reference to the people attending -- and the names of several Zinke aides who were also at the meeting.

Zinke also was to meet in May 2017 with the International Association of Drilling Contractors . The meeting was not listed on his calendar, but his scheduler included it in an email briefing to the secretary on his meetings for the week.

Thomas F. Farrell, the Toward the end of his second week in office, Zinke was scheduled to speak by phone for about 30 minutes withThomas F. Farrell,the president of Dominion Energy , a Virginia power company. That meeting was also revealed in an internal memo.

There are only two entries on Zinke's calendar that day: a daily meeting with senior staffers, and lunch.