2003 – The Center filed a petition to list Mexican garter snakes as threatened or endangered under the Endangered Species Act. The petition sought protection of the snake's habitat from livestock grazing and other threats, establishment of minimum instream flows in Southwest rivers, prohibitions on further introductions of nonnative fish and amphibians, and more funding for research and removal of exotics — actions likely to benefit myriad other species imperiled by the loss and degradation of Southwest rivers and streams.
2005 – The Center reached a settlement agreement with the U.S. Fish and Wildlife Service, requiring the agency to consider protection for the snake.
2006 – The Service denied Endangered Species Act protection to the Mexican garter snake, despite its own conclusions that the snake has been extirpated from 85 to 90 percent of its U.S. range, is declining, and is severely threatened by multiple factors in both the United States and Mexico.
December 27, 2007 – High-level Bush administration appointee Julie MacDonald resigned in the aftermath of an inspector general investigation — and just before a House congressional oversight committee public hearing — on her violations of the Endangered Species Act, censorship of science and intimidation of Fish and Wildlife Service staff. Official documents and a full-length report released to the media by the Center revealed that MacDonald, while assistant secretary of Fish, Wildlife and Parks, used her position to aggressively squelch protection of endangered species, including the Mexican garter snake. The Center filed suit against the Fish and Wildlife Service to overturn the agency's decision that the Mexican garter snake does not warrant protection as an endangered species.
May 28, 2008 – The Service announced that it would start a new status review to determine whether the snake deserves federal protection.
November 24, 2008 – The Service announced that the Mexican garter snake indeed deserves a place on the endangered species list — but instead of protecting the species, the agency made it a “candidate” for Endangered Species Act protection, claiming its listing was “precluded” by other actions to list species.
July 12, 2011 – The Center reached a landmark agreement with the Fish and Wildlife Service compelling the agency to move forward in the protection process for 757 species, including the Mexican garter snake.
February 2014 – The Center filed a cease-and-desist notice with the Federal Aviation Administration and Arizona's Department of Transportation to stop spending money for the construction of a new taxiway at the Sierra Vista Muni-Libby Airport. Initial work to support the taxiqway had already begun without an analysis of environmental harm, such as to the San Pedro River and its wildlife, such as the Mexican garter snake.
November 4, 2014 – The Center notified the UServiceof its intent to sue the agency under the Endangered Species Act over its livestock grazing program, which threatens two federally protected aquatic snakes including Mexican garter snakes.