(CNN) Interior Secretary Ryan Zinke held nearly 50 official meetings in May and June that, in sharp contrast to previous months, were so vaguely described on his official calendar that the public is unable tell what he was doing or with whom he was meeting.

For example, on June 11, according to his calendar, Zinke's morning consisted of a "video taping" and "external meeting," then two back-to-back "internal briefings," followed by an "external meeting." After a midday break, Zinke held an "external call" sandwiched between two "external meetings," followed by another "external call." The only names listed are those of staffers.

Previously, while hardly giving full details of his activities, Zinke's calendar entries had typically identified meetings by their topics, like an April 2017 calendar entry marked "Domestic Energy Producers Alliance Meeting,"or at least one attendee, such as a meeting with a particular senator. But the May and June entries this year include only sparsedetails about Zinke's activities besides the scheduled start and end times.

The missing titles in the most recently available calendars -- first spotted by the Center for Western Priorities, a nonpartisan conservation group that opposes Zinke's policy initiatives -- are outside the norm for Cabinet officials whose schedules are made public.

The Center for Western Priorities also noticed that the Zinke calendars no longer have text entered in the "description" portion of each entry, which typically provides additional details such as the names of those who had attended the meetings and a list of the topics discussed. It's unclear whether the scheduler is no longer putting information in that section or if Interior is withholding it. Until last September, Zinke's calendars had included those details.

later revealed: that the New York Republican had brought along several executives of a major tourism company that does business -- and is locked in a lawsuit -- with the Interior Department. This follows a CNN analysis in July that found Zinke's prior calendars omitted important details about his meetings. In one example, Zinke's calendar set aside time to meet with Rep. Chris Collins but failed to show what briefing documents prepared for the secretarylater revealed: that the New York Republican had brought along several executives of a major tourism company that does business -- and is locked in a lawsuit -- with the Interior Department.

After the CNN report in July, the Interior Department began publishing on Fridays a list of Zinke's meetings for that week, as well as advance notice of some of his public appearances. Previously, the department had taken a variety of approaches to disclosing Zinke's agenda.

In his first months as secretary, the department announced his public appearances in advance, a practice that tapered off last summer. More recently, the department has been uploading his calendars a month at a time to Interior's website, although those releases are made months after the fact. May and June, the months with significantly less detail, were released in late August, for example, in response to Freedom of Information Act requests.

The Interior Department said it would be "inaccurate" to view the changes to Zinke's calendars as a move away from transparency, pointing to meeting memos that contain the same information. But those memos are available only by filing a FOIA request.

"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," said spokeswoman Heather Swift.

The Center for Western Priorities said it believes it would be impossible for a Cabinet secretary to keep such a vague official schedule, and wonders if there is a "shadow calendar that's full of details Zinke doesn't want the American people to see," said Aaron Weiss, the group's spokesman.

"There is no way that this is the full extent of the secretary's calendar," Weiss said. "Someone must be keeping another record somewhere of who he's meeting with, and we've seen in emails that he gets a daily briefing, so we know there are other documents. They're just not providing it."

Swift said Zinke has only one calendar and that information on meeting attendees and topics is maintained on the meeting memos prepared by his aides. "These memos are available and regularly released to the public and media" when they are requested under the Freedom of Information Act, she said.

The omissions show that "Secretary Zinke specifically and the Trump administration generally have no respect for record keeping and transparency laws," said Norm Eisen, the Obama administration's ethics chief, who is now a senior fellow at the Brookings Institution think tank, board chairman of the nonprofit Citizens for Responsibility and Ethics in Washington, and a CNN political commentator.

"It makes a mockery of those standards to record the meetings but omit some of the most important information about them: who else attended. It also raises the question, what is he hiding?"

When he was asked by Sen. Tom Udall, a New Mexico Democrat, about public records requests at a Senate hearing in June 2017, Zinke testified that he intends to lead "the most transparent Interior" of his lifetime.

"He's delivered the exact opposite," Weiss said.