ABC News' Michael Falcone reports:

SAN DIEGO - California has two things the Republican presidential candidates want more than anything these days: plenty of wealthy GOP donors willing to write big checks and the largest treasure-trove of delegates in the country.

More than two months before voters in the Golden State head to the polls, the West Coast received some attention this week from both Mitt Romney and Rick Santorum. They each sought a fresh infusion of campaign cash and started laying the groundwork for the June 5 primary.

Last night, Santorum delivered a vehemently anti-Romney speech at the Jelly Belly Factory not far from Sacramento, an area that he called "the conservative heartland of northern California."

"California doesn't get a chance very much to play at presidential politics of late, but you will in this presidential primary," Santorum said, asking his audience to help his campaign "build a great organization here in California."

But it is Romney who already has the organizational advantage. Earlier this week, the former Massachusetts governor spent two days crisscrossing the state known as the ATM of presidential politics, holding fundraisers in San Diego, Los Angeles, Silicon Valley and Stockton.

"I need you guys to get ready, to organize your effort, to get your friends to vote, to collect some money, to get campaign contributions," Romney said at a medical device company in the hills above San Diego. "We've got a ways to go."

He has already locked up some of California's most high-profile Republican donors, including Hewlett Packard chief and former gubernatorial hopeful Meg Whitman and the owner of the San Diego Chargers football team, Alex Spanos, as well as several other members of the wealthy Spanos family.

Former California Gov. Pete Wilson is also a supporter. Wilson, and his wife Gayle, co-hosted a fundraiser for Romney in San Diego on Monday and in an interview with ABC News, he said Republicans were "united by their desire to make the president a one-termer."

Wilson said Romney's California swing was a sign of his strength among donors and political heavy-weights in an important state, a reflection of the former Massachusetts governor's prospects nationally.

"The primary has been expensive - not just in money - but also in time and effort," Wilson said. "Most people have said, 'enough.'"

Though Romney has opened up a significant delegate lead over Rick Santorum, it may not be until June 5 when California and four other states hold primaries, that the former Massachusetts governor finally reaches the 1,144 delegate threshold needed to clinch the nomination. (There's also a chance Romney still doesn't reach the magic number by then.)

But with 172 delegates at stake in California - more than any other state - Romney is expected to compete for every last one. Sources say he is already working with at local consultant who is helping his campaign put together a delegate slate. California awards its delegates on a winner-take-all basis by congressional district with 10 at-large delegates awarded to the statewide winner.

As a demonstration of Romney's hold on California, the campaign rolled out endorsements from businesswoman and former Senate candidate Carly Fiorina and California congressman and House Majority Whip Kevin McCarthy this week - two more additions to a long list of Golden State supporters.

As for Romney's rivals, former Gov. Wilson told ABC News, "the writing is pretty clearly on the wall."

"You won't hear him saying that," Wilson said of Romney, "but you will hear other people saying and thinking it."

Romney, who owns a beachfront home in an upscale community north of San Diego where he spent last weekend, also has the upper hand in the most recent polls. A Los Angeles Times/USC poll released earlier this week showed Romney with a 19 point lead over Santorum. Romney is at 42 percent compared to 23 percent for Santorum, 12 percent for Gingrich and 10 percent for Ron Paul.

"No one knows if it's going to get to California or not, but if it does, Mitt Romney is going to do extremely well," said State Senator Tony Strickland, a Romney supporter who is running for an open Congressional seat in a district north of Los Angles.

Strickland, who co-hosted a Los Angeles fundraiser for Romney this week and also supported him four years ago, warned that "people are underestimating the enthusiasm that Governor Romney has."

Ron Nehring, the former chairman of the California Republican Party and a respected GOP leader in the state, said that although Romney has opened up a clear delegate lead nationally, that has not deterred other campaigns from testing the waters.

"Suddenly there are a whole bunch of guys with 202 area codes in their cell phones making calls into California, asking questions for the first time about the political dynamic among Republicans here," Nehring said in a recent interview. The reason, he said, was the "big pot" of delegates available in both Texas and California at the very end of the primary calendar.

"It creates a disincentive for candidates to drop out," Nehring noted, "Why not roll the dice?"

At least among well-heeled donors, the chips seem to be falling with Romney.

Kelly Burt, the CEO of a San Diego-based self-storage company who served as a national finance co-chairman of Romney's campaign in 2008, is helping him raise money again this year.

"His support in California is widespread, and what you learn about Governor Romney is that those who have known him longest are his strongest supporters," Burt said in an interview. "You can't say that about all candidates."

It's much the same for Jim Righeimer, the mayor pro-tem of Costa Mesa located in heavily Republican Orange County. Righeimer, who described himself as "extremely socially conservative," said he was comfortable with Romney as the nominee.

"This is just dragging on," he said. "No doubt the donor base is saying, 'folks the fight is with the Obama administration.' We've just got to get this thing done."

Righeimer served on the host committee for Romney's Irvine fundraiser on Tuesday along with dozens of some of the biggest names on the Orange County GOP donor circuit who pledged to raise as much as $25,000 for Romney.

Righeimer said that many of his conservative friends who were previously backing Texas Gov. Rick Perry, the only other candidate who had any real donor base to speak of in California, had found their way to Romney.

But there are still opportunities for Santorum to pick up both money and support, according to Golden State political observers. The former Pennsylvania senator collected contributions on Thursday at the home of a dot-com executive in the leafy Bay Area suburb of Alamo.

Santorum's biggest base of voter support would likely come from the conservative inland areas of the state, especially in eastern San Diego county, Riverside and San Bernardino counties and in communities like Fairfield in the northern part of the state where he campaigned this week. Romney is better suited to the coastal population centers, including Orange County.

And whether or not California proves pivotal in the primary, the eventual GOP nominee will undoubtedly be back to tap the state's wealthy contributors during the fall campaign - especially if the nominee happens to be Romney.

"There is no Romney-mania deficit among certain segments of the active Republican community here," Nehring, the former GOP chairman, told ABC News. "He has an engendered a tremendous amount of loyalty from donors who will stick with him no matter what."