Colorado U.S. Attorney John Walsh says his decision to send letters ordering medical-marijuana dispensaries near schools to shut down has been met with an “outpouring of thanks and appreciation” from people who live near the shuttered businesses.

Walsh sent the letters earlier this year in the most aggressive action yet by federal prosecutors in Colorado against medical-marijuana businesses operating in compliance with state law — but in violation of federal law. His comments about the response came in a letter he sent Tuesday to Boulder District Attorney Stan Garnett, who last week sent a letter to Walsh asking him to back off on the crackdown.

In the letter to Garnett, Walsh reiterated that he decided to target dispensaries within 1,000 feet of schools after seeing evidence of a rise in youth marijuana use that coincided with the boom in medical-marijuana businesses in Colorado.

“We concluded that our responsibility — as federal law enforcement officials and also as Coloradans living in the very Colorado communities impacted by these alarming trends — required a response,” Walsh wrote to Garnett.

More than 20 dispensaries closed or moved after receiving letters from Walsh’s office. Walsh told Garnett he plans to send more letters to other dispensaries until no such businesses remain in Colorado within 1,000 feet of schools.

“This program,” Walsh wrote, “is not at the direction of Washington, D.C., but at my direction as U.S. Attorney and as a Coloradan.”

Colorado law places a 1,000-foot buffer between dispensaries and schools but also allows local governments to shrink that distance or grandfather in existing businesses. Medical-marijuana advocates say there is no evidence dispensaries — near schools or otherwise — are illegally selling to kids.

Last week, Garnett wrote to Walsh arguing that Colorado’s medical-marijuana regulatory system is working and urging Walsh to leave it alone.

“The people of Boulder County do not need Washington, D.C., or the federal government dictating how far dispensaries should be from schools, or other fine points of local land-use law,” Garnett wrote.

John Ingold: 303-954-1068 or jingold@denverpost.com