Per an e-mail from Boise Parks and Rec, this course is likely closed forever, but they are working with Gem State Disc Golf to find another suitable location...
This is a winter only course with one hole playing over a duck pond and three holes running parallel to the main streets (2 on Myrtle, 1 on Broadway).
From the Capitol Building: Capitol Building
700 W Jefferson St Boise, Idaho 83702, Head northwest on W Jefferson St toward N Capitol Blvd, Turn left at N 9th St, Turn left at W Myrtle St, Turn right at S 3rd St, Continue onto Julia Davis Dr.