Four women drove to vast desert wilderness along the southwestern border with Mexico. (Representational)

During the summer of 2017, when temperatures reached triple digits in Arizona, four women drove to a vast desert wilderness along the southwestern border with Mexico. They brought water jugs and canned food - items they later said they were leaving for dehydrated migrants crossing the unfriendly terrain to get to the United States.

The women were later charged with misdemeanor crimes. Prosecutors said they violated federal law by entering Cabeza Prieta, a protected 860,000-acre refuge, without a permit and leaving water and food there. A judge convicted them Friday in the latest example of growing tension between aid workers and the U.S. Border Patrol. Aid workers say their humanitarian efforts, motivated by a deep sense of right and wrong, have been criminalized during the Trump administration's crackdown on illegal border crossings. Federal officials say they were simply enforcing the law.

The four women, all volunteers for the Arizona-based aid group No More Deaths, were convicted after a three-day bench trial at a federal court in Tucson. They could face up to six months in federal prison.

Their trial coincided with a partial government shutdown now nearing its 30th day, the longest in the country's history. Negotiations have stalled as President Donald Trump stands firm on his demand for $5.7 billion in border wall funding, citing a humanitarian crisis at the southern border.

In his verdict order, federal magistrate Judge Bernardo Velasco said the women's actions violated "the national decision to maintain the Refuge in its pristine nature." Velasco also said the women committed the crimes believing, falsely, that they would not be prosecuted and, instead, would simply be banned or fined.

Catherine Gaffney, a volunteer for No More Deaths, said the guilty verdict challenges all "people of conscience throughout the country."

"If giving water to someone dying of thirst is illegal, what humanity is left in the law of this country?" she said in a statement.

The criminal charges stem from an incident on Aug. 13, 2017, when a federal wildlife canine officer found the women's pickup truck near Charlie Bell Pass, a historic site at Cabeza Prieta. Inside were water jugs, canned beans and several similar items. The officer spotted the women a few hours later. They admitted leaving food and water at the site, according to court records.

Natalie Hoffman, Oona Holcomb, Madeline Huse and Zaachila Orozco-McCormick were charged in December 2017. They said their work for No More Deaths was motivated by their religious convictions and a belief that everyone should have access to basic needs to survive, according to court records.

Federal prosecutors argued that the defendants should have been aware that leaving disposable items at the refuge is a punishable crime. During the trial last week, prosecutors said the women had admitted willingly violating federal law, the Arizona Republic reported.

In court documents, prosecutors pointed to a conversation between representatives of No More Deaths and a refuge manager who said officials prefer to use rescue beacons to help stranded migrants because they result in "actual rescues." Rescue beacons are scattered across the area for migrants to activate if they need help, officials said.

No More Deaths said rescue beacons result in only a small number of rescues. The group also points to the number of migrants who have died trying to cross the vast desert terrain in the region. More than 3,000 migrant deaths have been reported between October 1999 and April 2018, according to data gathered by Humane Borders and the medical examiner's office in Pima County, which covers part of Cabeza Prieta.

During the trial, one of the women, Orozco-McCormick, likened being on the refuge to being in a graveyard because of the number of migrants who have died there, the Arizona Republic reported.

The women are among several No More Deaths volunteers who are facing similar charges. Five others are scheduled for trial in February and March, the group said.

One of them, Scott Warren, is also accused of alien smuggling, a felony charge that No More Deaths claim was a retaliation for the group's activism. Last year, the group published footage showing Border Patrol agents kicking over water jugs left in the desert. One agent was seen emptying a gallon of water onto the ground. Warren was arrested shortly after the footage was published.

A Border Patrol spokesman told The Washington Post earlier that the agency is not targeting the group and is simply enforcing immigration laws. Court records say Warren met with two Mexico natives at a building known as "the Barn," located in the town of Ajo, Arizona, near the Cabeza Prieta refuge, and gave them food and water.

Warren told the Arizona Republic last year that his goal was to give food and medical care, not to smuggle migrants into the country.