Gov. Jerry Brown on Friday set May 21 as the election date to fill the seat of former state Sen. Michael Rubio, two weeks before Fresno city voters will be asked to go to the polls to vote on privatizing residential trash service.

Brown's announcement sets up a furious few months for the Fresno County Elections Office. This is supposed to be an off year for elections; now, the county will be running its portion of the state Senate special election, then holding the June 4 Fresno city referendum.

County elections chief Brandi Orth on Friday said the region has never seen two elections spaced so close, and called it an "extreme challenge." Orth said she's especially sensitive about confusion that Fresno city voters might have facing two ballots.

Even before they cast votes, more than a quarter of the city will be bombarded with fliers for both races.

Fresno County Supervisor Henry R. Perea said Friday he might be among the candidates.

Perea, 60, said he's been getting phone calls this week from state and local party officials. "It's humbling to think that people think that I'm a viable candidate," he said.

His son, Democratic Assembly Member Henry T. Perea of Fresno, had been considered an early front-runner two weeks ago after Rubio abruptly resigned his seat to take a job with Chevron Corp. But Henry T. Perea -- who would've had to move into the district -- announced last week he isn't running.

Only one person has announced plans to run for the seat: Democrat Alfred Benavides, a former Hanford Joint Union High School District trustee.

Three other Democrats appear to be considering candidacies. Leticia Perez, a former Rubio aide and newly elected Kern County supervisor, and Kings County Supervisor Richard Valle each addressed a Wednesday meeting of the Fresno County Democratic Central Committee.

Shafter City Council Member Fran Florez -- whose son Dean Florez held the seat before Rubio -- didn't address the Fresno Democrats because her daughter had a baby that morning, but appears to be interested in running.

Former Assembly Member Nicole Parra of Bakersfield this week dispelled talk of her being a candidate. Parra, who served in the Assembly as a Democrat but is now registered as "no party preference," was the top hope of Republicans looking to steal the seat. Parra likely would have caucused with the GOP.

The district that selects Rubio's replacement will be state Senate District 16 as it was between 2002 and 2012. Political Data Inc., a firm that collects and distributes voter information, said the district is 50.7% Democrat and 28.6% Republican, according to data as of Feb. 22.

It is unknown who the Republicans might rally behind, but some names mentioned include Pedro Rios of Delano, who lost a tight race for the 32nd Assembly District seat last fall; Kerman Mayor Gary Yep, who said he's looking at a run; Bakersfield City Council Member Russell Johnson; Hanford farmer Andy Vidak, who fought a pitched 2010 congressional battle before falling to incumbent Jim Costa; and Fresno County dairyman Johnny Tacherra, who challenged Costa last year.

If, as expected, none of the candidates running May 21 win a majority of the votes, the top two will advance to a run-off July 23.

That only adds to the Fresno County Clerk's Office's burden.

"I don't believe in the history of this department has this office been required to conduct two good-size elections within a couple weeks of each other," Orth said Friday. "Logistically for us, this is an extreme challenge."

Her office has to not only prepare election materials for the contests, a process that's normally begun four months before a race, but also line up polling sites and precinct officers for the two elections.

And then there's the confusion voters are bound to encounter. About 74,000 Fresno residents voting on the trash issue will also vote in the special Senate race. For many, that means receiving two mail ballots at about the same time.

"We're looking for different ways to identify our vote-by-mail envelopes," Orth said, noting that bright colors or big print on the mailers are possibilities. "Voters need to be very aware of what ballot goes in what envelope and what the timelines are to do that."

The cost of the Senate special election will fall on the counties, Orth said. While she's yet to calculate the expense for Fresno County, she figures it will be at least a quarter of the $2 million that a countywide election generally costs.

The city of Fresno will pay for the June 4 election, a cost estimated to be $750,000 to $950,000.