When I discovered the Cedarville Esker last week, placing another cache ('Near the Esker') an hour to the north of Guelph, it reminded me that a small remnant of the Guelph Esker still exists. It used to run several miles though southwest Guelph; now only about 150 metres of it can still be seen inside Preservation Park. The rest has all been mined out for gravel long ago.
Parking is in the small lot beside the sports field on the north side of Kortright. Cross the road (carefully!) and enter the trail at the west end of the conservation area, right beside the first house (not the main entrance further east). Don't take the main path that goes right along the fence, but take the one that veers to the left uphill. For the next 180 steps or so, you are walking along the top of the esker ridge.
An esker is the gravel from an old riverbed that was once inside a glacier, held in place by walls of ice. When the glacier eventually vanished, a sinuous ridge of gravel was left behind across the landscape. You can clearly see the steep sides of this little remnant esker as you walk along it.
The letterbox cache is off the trail, downslope, hidden in the roots of a big yellow birch. Count 136 steps from the sidewalk, or 43 backwards if you walk all the way through to come out at the main trail; look downslope. And watch for muggles, a busy trail at times.
Yellow birch seeds don't germinate and grow easily under the leaves on the forest floor; they are far more likely to germinate successfully in the top of an old stump. Then the tree grows up and the roots grow down around the stump; when the stump rots away, the tree is left standing on several 'legs' - this is a great example.
If you carry on to the main trail again you'll come out to a clearing behind a large stormwater pond. You can continue south or turn left to head back to the main part of Preservation Park; either way there are other letterboxes and caches to be found.
Check the Hanlon Creek trail maps on my blog, Hanlon Creek Journal, Jan. 26, 2010 posting.