Wachter and others cite an American Enterprise Institute estimate that a national capacity of 750,000 tests per week would provide adequate monitoring to reopen schools and businesses. By that standard, California's population of 40 million would need to conduct about 90,000 tests per week. The state has conducted roughly 177,000 total tests so far and is quickly adding capacity through private, academic and public labs.

"The biggest factor by far is the diminishing number of cases; that swamps everything. If it's still hot in your community, then you're not ready to move on even if you have all the tests in the world," he said. "Let's say it's four to five weeks from now; I think we will have sufficient testing capacity to meet that need."

In Contra Costa County, a suburban landscape east of Oakland where eight people have died, health officer Chris Farnitano pointed to testing as the weak spot that could force restrictions to remain in place longer. Once the county has a better grasp of infections, he said, it can lift social-distancing measures in stages.

Some restrictions — such as prohibiting large gatherings and protecting high-risk residents — aren't going away soon, Farnitano said. “Community cover-your-face restrictions may be the cultural norm for a long time,” he said.

Experts also have a hard time seeing large gatherings resume. Santa Clara County, home of the National Football League's San Francisco 49ers and two other pro sports franchises, banned gatherings of 1,000 people or more a week before its shelter-in-place order.

Jeff Smith, a physician and the executive officer of Santa Clara County, said this week he wouldn't expect sporting events to resume by September — “and we’d be lucky to have them by Thanksgiving.”

George Rutherford, an infectious disease specialist and epidemiologist at UCSF, expects a staggered return-to-work strategy with certain sectors like manufacturing returning first — but not all at once.

But he did not expect the “attack rate," or the percentage of people to contract the virus, to be high enough to confer widespread immunity.

“We’re not going to have enough people with antibodies to do anything,” he said. “We’ve kept people from getting infected.”

After the restrictions begin, he said, the region will have to go back to the tactics of strict isolation of infected individuals and contact-tracing that were used at the beginning of the pandemic to help quash hotspots as they arise. Rutherford and others at UCSF are working with San Francisco health officials on improving their contact-tracing procedures, which involves determining the source of infection and who else may have been exposed.

"There's so many good people working on this problem right now that we are certainly capable of doing this fairly quickly," Swartzberg said. "The problem is that we have no nationally concerted plan to accomplish this, and so it's being done in a very spotty fashion."

A sign at the entrance to the Orinda Care Center in the San Francisco Bay Area.

Santa Clara County has been ahead of the nation throughout the crisis. The county in early March tested 226 patients with respiratory symptoms at four urgent care centers to gauge the spread of Covid-19 in the community, according to a CDC report. Testing found that 11 percent of patients who did not have the flu tested positive for the virus, an early finding that helped convince the six Bay Area counties and the city of Berkeley to impose their shelter-in-place orders on March 16.

Just as counties led the way into social distancing, they're likely to lead the way out. State and local officials in California spurned President Donald Trump's assertion weeks ago that the U.S. could open up by Easter, and Newsom disagreed with the president that the National Football League could resume in September.

"You're going to begin to see regions make the decision based on their own reading of the numbers and their own expert guidance," Wachter said.

There are reasons for hope. In Santa Clara County, Cody told the Board of Supervisors that original projections of 50,000 coronavirus cases in the county absent any mitigation measures have fallen below 12,000 — and could even be as low as 2,500.

She also emphasized that the number of days it takes Covid-19 cases to double has dropped from about three days in early March to around two weeks now, a dramatic slowing of the growth rate.

Absent reliable testing data, the death rate is a key indicator of when counties should start to lift restrictions, said John Ioannidis, professor of medicine, epidemiology and population health at Stanford University. Questions also remain about whether the virus will recede in the warmer months, like the seasonal flu, as well as how much immunity is conferred by having been infected.

If the virus is deemed less deadly than previously thought, as Ioannidis expects, public pressure to return to normal may increase.

“I feel very optimistic the best solution will not be to continue to lock down and shelter in place," he said. "There’s a huge gradient between mass gatherings and many other interim steps that would be easy to track.”

He said he worried about the long-term implications of social distancing and unemployment on lives. “It’s not just suicides,” he said. “Cardiovascular disease goes up, people will lose health insurance. They will not be able to get care for common things.”

The governor has not made his modeling accessible to the public, aside from showing a chart last week with a flatter curve than originally expected. Some in California have questioned Newsom's conservative projections.

Ioannidis said he believes Newsom's model relies on an infection rate as high as 80 percent — a worst-case scenario that Ioannidis says is "unrealistic" and based on early observations elsewhere that have since been walked back. He also said California should not extrapolate from New York, given "the vast majority of the world is not as dense and intermingling."

"That has absolutely no science to back it," Ioannidis said.

To be fair, Newsom's model has changed. The governor explained this week that California's curve has lengthened and flattened, meaning that the state should see fewer cases and deaths leading up to a May peak.

And the governor may not want to speak as candidly as scientists and doctors, knowing that residents could interpret positive news as a sign that it's OK to leave the house again. He flipped a question this week on when the state might reopen into an opportunity to hammer home his social-distancing message.

"It depends on you," he said. "It depends on 40 million others in the state of California, and their commitment to following through on the stay-at-home orders, their commitment to have appropriate face coverings."