A Look at the Emerald Necklace Trails Master Plan The mission of Groundwork Jacksonville is to build and connect Jacksonville’s Emerald Necklace. When complete the Emerald Necklace could encompass as much as 19-miles of new trails, greenspace, parks and waterways encircling the urban core and linking at least 14 neighborhoods and downtown to Hogans Creek, McCoys Creek, the S-Line Rail Trail and the Northbank and Southbank riverwalks.