They also objected to the proposal arising partway through the year when the council could not weigh it against other projects.
McAdams said the issue came up now because the bank, which obtained the property from Talisker in a foreclosure proceeding, gave purchase proponents until mid-March to raise the money.
Faced with that challenge, Park City Councilman Andy Beerman said, 72 percent of his city's residents voted for a bond proposal to purchase the land. Summit County, Salt Lake City and nearly a dozen nonprofits got together to boost fundraising efforts, he added. To date, the organizations have raised another $10 million from 1,700 donors.
"It's really taken a village," Beerman said, contending development in Bonanza Flats will have a major impact on Salt Lake County's watershed since runoff from there goes into Deer Creek Reservoir, which supplies water to the Wasatch Front.
"This isn't just a preservation choice, but a practical one," he said. "Leverage your money. Save yourselves some big headaches in the long run."
McAdams found two sources of money in the county's $1.1 billion budget to fund the contribution without tapping the general fund.
The county could use unanticipated revenue from its share of the state's recent agreement with Amazon to collect online sales taxes owed by Utahns, he said. It also could divert some money from an earlier bond issuance for the new district attorney and health department buildings, because those projects recently qualified for $2.4 million in New Market Tax Credits.
McAdams also said the county is likely to face higher expenses if Bonanza Flats is developed and pressure mounts to keep Guardsman Pass open year-round, generating considerably more traffic in Big Cottonwood Canyon.
Speaker after speaker implored the council Tuesday to provide the clinching cash, recounting memorable personal experiences there.
The only speaker against funding the Bonanza Flats purchase was Heather Williamson of the conservative lobbying group Americans for Prosperity, who called a mid-year appropriation "arbitrary."
Her argument resonated with council Republicans.
"This area is beautiful and a great benefit to the community," said Aimee Winder Newton, but coming up in mid-March "jades our viewpoint. This isn't the right time to look at expenditures when we can't look at it holistically."
Richard Snelgrove, an avid hiker who knows Bonanza Flats well, said he could not justify spending Salt Lake County taxpayers' money in Wasatch County when so many parks, trails and other recreational assets in his own county need attention.
And Michael Jensen, who said he represents west-side residents with plenty of worthy projects too, said "it's a great endeavor, but sometimes you have to say no. We have to weigh priorities."