The route is (if starting from Fenders in Polk City): 3rd St/Sheldahl Dr north to the High Trestle trail (at The Oasis), north to Slater then east on the Heart of Iowa Nature Trail to Huxley and Fenceline Beerlab (under the water tower), back on the Iowa Nature Trail to Slater then South on the High Trestle Trail to Firetrucker in Ankeny, then the last leg back to Polk City (west on 1st St to the Neal Smith Trail then head north.)
The "loop" is about 35 miles, but YMMV!