As temperatures in Arizona shot toward their summer peaks, so did the state’s coronavirus crisis. Lines for drive-up testing snaked for blocks in June. Hospitals were running out of beds, bodies were being stored in coolers, and the state’s per capita caseload topped global charts.

But by mid-August, the Southwest hot spot made a remarkable reversal. Cases plummeted 75 percent.

Arizona has maintained relatively low case numbers since, but they are now creeping to levels seen just a few weeks before its summer surge. And as a conflagration engulfs the Midwest and Mountain West, public health experts and elected officials in Arizona are pleading with residents to maintain mitigation measures they say played a critical role in beating back the virus and hold lessons for other states — including mask mandates that covered 85 percent of the population.

“The mask ordinances should stay in place until we get pretty wide distribution of the vaccine,” said Will Humble, a former state health department director who now leads the Arizona Public Health Association. “The return on investment is off the charts. The only thing that it costs is political capital.”

That emphasis on face coverings echoes intensifying calls by public health experts nationwide amid growing evidence of masks’ effectiveness in reducing transmission — and signs that a pandemic-weary population and battered economy may not tolerate widespread shutdowns.

Deborah Birx, coordinator of the White House coronavirus task force, has been touring states and chiding those where mask use is low. Democratic presidential candidate Joe Biden and former Food and Drug Administration commissioner Scott Gottlieb have advocated for a national mask mandate. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, has also urged mandates, recently calling mask-wearing and social distancing simple measures that may be “the next best thing” to shutdowns that are unlikely to be repeated.

Some local governments in hard-hit red states where masks have been especially contentious are heeding the call. In recent days, mandates were passed in Coeur d’Alene, Idaho, and the North Dakota cities of Bismarck and Grand Forks.

In Arizona, some jurisdictions are lifting mask mandates, fraying nerves among some observers who say such loosening is premature.

“I’m becoming more of a firm believer that face masks are a truly effective intervention in this particular outbreak and should be considered our first line of defense,” said Joe K. Gerald, a University of Arizona public health researcher who tracks coronavirus trends in the state. Places without them, he said, are “shooting themselves in the foot because wearing face masks can protect individuals but also reduce the spread to others and allow more economic activity and social activity.”

Arizona’s comeback did not coincide solely with masks. Gov. Doug Ducey (R) in late June limited public events and temporarily closed bars, gyms and theaters, the Centers for Disease Control and Prevention noted in a recent report that highlighted the state’s recovery.

Arizona never enacted a statewide mandate, and for weeks in the spring, Ducey refused to allow local governments to impose their own. He relented in mid-June following pressure from mayors, county leaders and medical professionals. Dozens of jurisdictions, including conservative towns where public opposition was fierce, promptly passed mandates. The decline in cases began two weeks later, the CDC report said.

In August, according to survey data analyzed by the University of Washington’s Institute for Health Metrics and Evaluation, more than 80 percent of Arizonans said they always wore a mask in public. Now, the institute says, that has fallen to about 70 percent, slightly above the national average.

Ducey on Oct. 23 lauded his state’s coronavirus response in a Twitter thread proclaiming that “masks work” and that he had “swiftly” allowed local leaders to impose mandates.

“I would not characterize the governor’s response as swift,” Phoenix Mayor Kate Gallego (D) said in an interview, adding that she thinks a statewide mandate is needed. “I would like all elected officials to send a consistent message that masking is important.”

The CDC report on Arizona emphasizes that it is not clear whether mask mandates, bar and business closures or gathering limits caused the summer case decline — only that they were strongly correlated. Nor does it attempt to quantify which measure was most important. Other factors, including other states’ policies or residents’ personal decisions, may also have played roles, it says.

“A lot of community-based education was done and efforts to increase testing,” said Saskia Popescu, an infectious-disease epidemiologist and adjunct professor at the University of Arizona. “It wasn’t just a mask mandate, which is very important, but it’s all of these things working collectively together.”

A growing number of studies have found that mask-wearing can reduce the risk of transmitting the coronavirus and the severity of covid-19, the illness it causes — evidence masks protect the wearer and others. A CDC study published in October found that people who wore masks were more likely to engage in social distancing and had a lower risk of infection when exposed to someone infected with the virus.

Whether mask mandates work is less certain. A June study found lower growth in coronavirus rates in states that passed mandates in the spring, possibly preventing more than 200,000 deaths. Skeptics point to states such as Wisconsin and Montana, which have mandates but are suffering through their worst outbreaks yet.

“It’s hard to try to isolate out this was the mask mandate, this was the outcome,” said Stefan Baral, a Johns Hopkins University epidemiologist, who added that he thinks public health mandates should be local.

Humble said the mandates “normalized” masks in Arizona. But he and other experts in the state say that even if the evidence for mask mandates is circumstantial, now is no time to do away with them.

Gerald’s weekly coronavirus report noted Wednesday that transmission is increasing in all age groups in Arizona and that along with measures to address “quarantine fatigue,” mask ordinances will remain crucial.

“It’s not a very long distance between where we are now and a really difficult time,” Gerald said. “It’s much like we’re holding a loaded weapon, and if we treat it carelessly, it can go off and hurt us.”

And yet two months after many bars were allowed to reopen at lower capacity, some Arizona jurisdictions are lifting their mask mandates. The mayor of Scottsdale, adjacent to Phoenix, said last month the city’s mandate had worked and was being rescinded, drawing criticism from the local Chamber of Commerce and major health systems. The city is still subject to a county mandate.

Tom Morrissey, mayor of the small town of Payson and former chairman of the Arizona Republican Party, announced a mandate in June with what he called “mixed feelings.” He lifted it in September in response to the state’s reduced caseload. Now, rising cases in surrounding Gila County are making him reconsider, he said.

“Somebody’s got to make a decision on it. And that somebody in Payson is me. So I am looking at it really closely,” Morrissey said, though he emphasized that any new measures would involve more than masks — and must have public support. “Viability is the thing.”

A mandate in the town of Cottonwood still stands months after Mayor Tim Elinski imposed it, overruling the city council, defying protesters and telling a local newspaper, “If history proves me wrong, then I will graciously apologize.” When reached by phone recently, he declined to speak to a reporter, saying the measure remained deeply controversial.

A Cottonwood Council member who backed the mandate, Ruben Jauregui, said the mayor did the right thing. But Jauregui worries residents are lapsing. During a recent trip to a tire shop, Jauregui was disappointed to see no other customers wearing masks.

“Common sense tells you this isn’t over,” Jauregui said. “The second wave is here.”

Robin Schaeffer, executive director of the Arizona Nurses Association, has called on local governments to stick with mask mandates. Hospitals are in a better position to deal with rising caseloads than they were in the spring, but nurses are exhausted, she said.

Arizonans, Schaeffer said, “are covided out. They’re tired. But you can’t stop now. Because the truth is that this virus is nowhere under control.”

On a recent evening in downtown Chandler, a Phoenix suburb subject to a county mask ordinance, people strolled through the downtown, taking advantage of the recently cooled weather.

Some wore masks; others did not. Amanda and Unica Buitizon realized they’d forgotten theirs as they approached SanTan Brewing. After going back to their car to retrieve them, the Chandler couple ate pizza and drank beers outside.

Unica Buitizon, a 21-year-old project manager at a telehealth company, said he questions masks’ effectiveness and bristles at the mandate.

“Only if I’m forced. I will literally go into a store with a mask in my hand and wait until they tell me to put it on,” he said.

Amanda Buitizon, a 22-year-old masseuse, said she is not especially concerned about catching the virus. But she said she is willing to wear one for the sake of others.

“I’m not scared about it, but I’m doing it for other people,” she said.

Edwin Galindo, who works at an auto shop as a fabricator, got off a bus with no mask on. Galindo, 45, said every other passenger was wearing one, so he wasn’t concerned.

These days, Galindo said, he wears masks more often than during Arizona’s summer spike, because more people he knows have had friends or relatives contract the virus. He said he makes sure his young children wear them — and they often remind him to do so, too.

Karin Brulliard reported from Washington. Jeremy Duda reported from Phoenix.