Spread across Zion National Park is a patchwork of private parcels, complicating park management and enabling potential trophy homes to rise in otherwise wild landscapes.

One of those “inholdings,” a 35-acre piece at Firepit Knoll near Zion’s Hop Valley trailhead, is to become part of the park under a deal announced Monday by the nonprofits Trust for Public Land and National Park Foundation.

”The investment we make now will deliver for many years to come,” said Diane Regas, the trust’s president. “We want national parks to be for everybody. They are the most majestic public lands and essential to us as a country. If the parks are whole, we can manage them for everybody.”

The trust sealed a deal to buy the property for $354,000 in private money, some coming from a park volunteer and avid hiker named John Donnell. The deal will help protect the Kolob Terrace viewshed and habitat corridors in the northwest part of the park, according to Zion Superintendent Jeff Bradybaugh.

Still, 3,400 acres, covering 2 percent of Utah’s marquee park, remain private in 32 parcels, many on Kolob Terrace, a late addition to the park established in 1919. One inholding covers the the Hop Valley Trail, potentially obstructing the so-called Trans-Zion trek, the only route connecting Kolob Canyons with the rest of the park.

“We strive to work with those owners to make sure we are good neighbors and they are as well,” Bradybaugh said. “Our biggest concern is if those lands are developed. Some could be subdivided.”

The Trust for Public Land is also trying to secure easements on parcels just outside the park’s eastern boundaries because they provide access to Zion’s most-coveted hikes. For a few days recently, the park stopped issuing permits for the Zion Narrows after property owners put up signs announcing a “trespassing fee” to cross their land.

The owners have been trying to sell a conservation easement that would permanently secure public access but were frustrated with the federal government’s low assessment of the land’s fair-market value. Negotiations are ongoing.

“As land values have gone up, it makes it that much more difficult to acquire these properties, because the funding isn’t available to pay fair-market value,” said Cory MacNulty, a National Parks Conservation Association program director. “The only thing protecting those properties is county zoning.”

Despite mounting visitation pressure, Zion has acquired only a single inholding in the past decade. In 2012, The Trust for Public Land secured a deal for a 30-acre parcel at the base of Tabernacle Dome, also on Kolob Terrace, with an anonymous $825,000 donation. The parcel was deeded to the park, which dismantled the structures on it.

Most of the [Kolob inholdings] are close to the [Kolob Terrace] road and are very visible,” said MacNulty, who helped orchestrate the Tabernacle Dome deal. “We tend to focus on the parcels that are going to have the biggest impact on resources and visitor experience. Some of these are inside designated wilderness.”

About 58 percent of Zion’s inholdings, or 2,000 acres, are currently used in ways that align with park management, according to Zion’s “State of the Park” report. Many are used for grazing, which isn’t a problem until the cattle “trespass” onto parklands, particularly in Hop Valley, potentially degrading water quality and sensitive ground near streams and springs.

“Agricultural uses are fairly compatible with the rural nature and wilderness values of the park,” Bradybaugh said. “Many [parcels] have been in families for decade and decades and are much cherished by the families and are managed in ways that take care of those parklike qualities.”

But those holdings could wind up with new owners who have different plans, and some have no obstacles to development. A yellow mansion went up behind a gated driveway near Firepit Knoll a few years ago.

In past decades, the National Park Service wielded the power of eminent domain to buy park inholdings and force out their residents. These days, the agency and its surrogates will attempt to acquire inholdings from only willing sellers. Zion National Park policy calls for acquiring any inholding that an owner is interested in selling, but money is tight.

“We are in regular contact with those landowners,” said the trust’s Southwest director, Jim Petterson. “You have to be in a position to jump when an opportunity arises.”

Public money for such purchases typically comes from the Land and Water Conservation Fund, a pool of federal offshore oil and gas revenue used to buy private land with recreational and natural values.

But Congress has long underfunded the program. Last week, lawmakers let the fund’s authorizing legislation expire after 50 years, throwing a cloud of uncertainty on what is regarded as one of the nation’s most successful, though little-known, conservation programs. Liberal politicians and environmental groups are now clamoring for the fund’s permanent reauthorization, demanding full funding.