The race for District 4 supervisor is headed for a runoff between Dennis Rodoni and Dominic Grossi, who separated themselves from the crowded field of eight candidates in Tuesday’s primary election. Mr. Rodoni secured 30.67 percent of votes with 2,494, while Mr. Grossi notched 26.06 percent with 2,119 votes. Wendi Kallins came in third, with 16.8 percent, or 1,366 votes.

Tuesday’s primary captured a 41.38 percent voter turnout, which looks to be Marin’s lowest primary turnout since 2000. The county’s Election Department will post finalized results on Friday.

Since neither Mr. Rodoni nor Mr. Grossi garnered more than half of the votes, a runoff election will be held on Nov. 8. A local debate between the two candidates is tentatively scheduled for September, in advance of a hotly anticipated election to replace West Marin’s 20-year representative on the Marin County Board of Supervisors, Steve Kinsey. 

An Olema contractor with a lengthy public-service resume, Mr. Rodoni has long advocated for environmental causes. Still a longtime board member of the North Marin Water District, Mr. Rodoni has served on boards for the Coastal Health Alliance, West Marin Senior Services and the Point Reyes National Seashore Association. He garnered endorsements from a slew of elected officials, farmers and ranchers, and the Sierra Club, and led in campaign donations with over $60,000.

Mr. Rodoni has voiced support for ranchers in the Point Reyes National Seashore, saying he is in favor of 20-year lease extensions and a degree of diversification. At a candidates forum this spring, Mr. Rodoni called on elected officials to ask the environmental groups that have sued the National Park Service over ranching on Point Reyes to withdraw their suit, sit down and find a “simple solution.”

In letters to the editor in the Light, Mr. Rodoni has received praise for his record of environmental conservation, including his efforts to restore the Giacomini Wetlands. Other letters, meanwhile, criticized him for incorrectly advertising individuals who did not endorse his campaign and for his position on Drakes Bay Oyster Company.

In an op-ed piece penned for High Country News in 2009, Mr. Rodoni slammed Senator Dianne Feinstein for drafting legislation that would have directed the Interior Department to award a lease extension to the oyster company. He viewed the move as an affront to the public’s right to have a say over national parklands.

Mr. Grossi, meanwhile, is a fourth-generation Novato dairyman viewed by many as a champion for Marin’s ranching community, and said he fought alongside oyster company owner Kevin Lunny to secure a lease extension and keep the business from closing. In recent months, Mr. Grossi has blasted the environmental groups that are suing seashore, and has said elected officials should draft legislation that would protect ranches.

Mr. Grossi has served on the board of the Marin Agricultural Land Trust and is a former president of the Marin County Farm Bureau. His endorsers include several county departments, the Marin Independent Journal and former longtime District 4 Supervisor Gary Giacomini. He raised just under $50,000.

On affordable housing, both candidates have called on the county to ease restrictions on second units and provide protections for worker housing to help shore up West Marin’s dwindling affordable-housing stock. Mr. Rodoni, however, has stopped short of voicing support for regulations on vacation rentals until the county gathers further data on the impacts of vacation rentals. Mr. Grossi—as well as all the other candidates—would immediately support any such legislation.

Few letters turned in to support or oppose Mr. Grossi’s campaign, though one letter writer noted Mr. Grossi advertised Santa Cruz’s Pigeon Point Lighthouse in his mailed flyer, rather than the Point Reyes Lighthouse.

Wendi Kallins, the Forest Knolls founder of Safe Routes to Schools who came in third, was notable as a staunch housing, traffic advocate and systemic thinker. She was saluted in a letter to the editor as the only candidate who attended a recent West Marin forum on affordable housing, and she received endorsements from many city councilors and school superintendents, the Marin Democratic Party and the Light. She raised around $25,000.

Rounding out the supervisorial candidates were Al Dugan, a risk management consultant in Novato, with 720 votes; Alex Easton-Brown, a retired social scientist in Lagunitas, with 453; Tomas Kaselionis, an operations supervisor for the Federal Emergency Management Agency in Novato, with 379; Brian Staley, a construction manager in Woodacre, with 316; and Mari Tamburo, a musician from Mill Valley, with 271.

The runoff race between Mr. Rodoni and Mr. Grossi appears poised for a heated contest, as the two candidates have butted heads in recent months over campaign signs at and around the Olema Campground. Just a stone’s throw from Mr. Rodoni’s home, the campground has hosted a flurry of Mr. Grossi’s signs, some of which have been vandalized. Though he once called Mr. Grossi to complain about the signs, Mr. Rodoni brushed aside accusations of involvement with vandalism and noted that a dozen of his own signs between Olema and Point Reyes Station disappeared last month.

Campaigns for both Mr. Rodoni and Mr. Grossi have put out hundreds of signs throughout District 4, which encompasses West Marin, Novato and portions of Southern Marin. Under county code, candidates are required to remove their signs within 10 days after the election.