WASHINGTON — Yosemite National Park suffers from a "toxic" leadership environment that has prompted numerous employee complaints and raises questions about Superintendent Don Neubacher's future, a congressional hearing revealed Thursday.

The allegations are serious enough that the Interior Department has launched a formal investigation, which is just getting underway.

In a sustained and withering blast at the management of one of the nation's most beloved parks, Yosemite's fire and aviation management chief Kelly Martin cited repeated instances of "bullying, gender bias and favoritism" at the park she has worked at for the past decade.

"People do fear they aren't safe in bringing issues to management," Martin told the House Oversight and Government Reform Committee, characterizing Yosemite's as a "hostile work environment."

As an example, Martin described what she said was her "humiliating" treatment by Yosemite management during the park's response to the high-profile Rim fire in 2013. Martin said she wasn't allowed to do her job, significantly undercutting her authority with her co-workers.

Underscoring Martin's alarming message, the committee's chairman, Rep. Jason Chaffetz, R-Utah, disclosed that "at least" 18 different Yosemite employees have lodged complaints about working conditions at the park. Chaffetz cited one investigator's characterization of the Yosemite work conditions as "horrific."

"These employees lay the blame at the top," Chaffetz said.

Michael Reynolds, the National Park Service's deputy director for operations, testified that there is an "active investigation" underway into the complaints about Yosemite management. The park service conducted the initial Yosemite inquiry in August, and the investigation has subsequently been taken over by the Interior Department's Office of Inspector General, Reynolds disclosed.

Reynolds did not offer further details about the scope and timing of the probe.

At the same time, Reynolds insisted the agency is undertaking a series of broader management reforms. In August, the park service announced a number of leadership changes. The current director, Jon Jarvis, is scheduled to retire next year.

"This kind of change is neither easy nor fast," Reynolds said, adding that "actions are underway."

A career park service employee, Neubacher has served as Yosemite superintendent since 2010. The park's deputy superintendent position has been vacant for several years, Martin noted.

"Some employees have left Yosemite National Park or the National Park Service altogether due to the current work environment where belittling, favoritism and public questioning of one's professional credibility is pervasive," Martin said in her written testimony.

The two-hour, 15-minute hearing Thursday afternoon followed up on an earlier public grilling last June, when the oversight committee first put a spotlight on a highly critical report from the Interior Department's Office of Inspector General.

Deputy Inspector General Mary L. Kendall cited complaints about sexual harassment at Grand Canyon and Canaveral National Seashore, alleged ethics violations by Jarvis in writing a book without seeking approval and misuse of park housing by Yellowstone National Park's former chief ranger.

"The department does not do well in holding accountable those employees who engage in mismanagement and/or misconduct that violates laws, rules, and regulations," Kendall told the panel in June.

In a worrisome sign for park service officials, moreover, committee members have largely united in their ongoing agency probe. On Thursday, they avoided the partisanship exemplified earlier in the day when the committee voted along strict party lines to hold one of Hillary Clinton's aides in contempt for failing to appear on an email investigation.

"No employee of the federal civil service should ever feel afraid to come to work," said Rep. Elijah Cummings of Maryland, the committee's senior Democrat.

Lawmakers from both parties periodically raised their voices as they berated Reynolds, demanded action and asked about firing officials to stop the kind of alleged misbehavior described by Martin and Brian Healy, fisheries program manager at Grand Canyon National Park.

Martin, for one, told the committee that in 1987, while working at Grand Canyon, she was the victim of a "peeping Tom" who was also a park service colleague. She did not file a formal law enforcement complaint against the man, who continued working for the agency for many more years.

"I was just starting off my career," Martin recounted, and "I did not want to make this an issue."