"The Administration should abandon this proposal," DeSaulnier wrote. "This proposal is antithetical to the values of our community."
The naval station is unsafe, as it's located next to an Army ammunition and explosives depot, DeSaulnier noted. Environmental cleanup of the area is still underway, and there's no sewage system or power, he stressed.
"Rounding people up and forcing them to sleep in tent cities among tens of thousands of others is inhumane and cruel at the most basic levels," DeSaulnier wrote.
Representatives Ami Bera (D-Elk Grove), Anna Eshoo (D-Palo Alto), John Garamendi (D-Fairfield), Jared Huffman (D-San Rafael), Ro Khanna (D-Santa Clara), Barbara Lee (D-Oakland), Zoe Lofgren (D-San Jose), Doris Matsui (D-Sacramento), Jerry McNerney (D-Antioch), Jimmy Panetta (D-Salinas), Jackie Speier (D-San Mateo), Eric Swalwell (D-Castro Valley) and Mike Thompson (D-Napa) signed onto a group letter.
Several of those members traveled to Texas last weekend to visit facilities run by the federal government at the border that housed children separated from their parents.
One of them was Garamendi.
"This is nonsense," the North Bay congressman said in an interview Tuesday.
"Are you guys serious? Are you really thinking about doing this? If so, let us know so we can jump up and down on you and stop it," said Garamendi, a member of the House Armed Services Committee.
Last Friday, Time magazine, citing a draft memo it obtained, reported that the Navy was considering converting the Concord facility into a camp to house 47,000 immigrants detained at the U.S.-Mexico border.
That story set off strong opposition from local leaders and immigration advocates.
Anna Roth, director of Contra Costa County Health Services, issued a statement calling the proposal dangerous and immoral.
In the hours after the Time story broke, military officials would not confirm that the Concord base was being floated as a potential detention location.
"The Department of Defense (DOD) is conducting prudent planning and are looking at all available regions should DHS (Department of Homeland Security) ask for assistance in housing adult illegal immigrants," said Johnny Michael, a DOD spokesman, in an email then.
"At this time there has been no request from DHS," Michael said.
But on Wednesday the Navy inched forward on confirming the story.
"In order to inform potential senior leader discussion around this topic, Navy planners proactively pulled together a list of options that could be considered," said Capt. Gregory Hicks, Chief Navy spokesman, in an emailed statement.
"The memo is strictly pre-decisional and meant for informed deliberation by senior leaders," Hicks said.