A geodetic survey is a collection of accurately measured points on the Earth's surface. The history of geodetic surveys in Canada reaches back to the late 1800s with the first precise vertical measurement being taken in Quebec in 1883. Canada's geodetic survey program really took off in 1905 and I encourage you to read more about 100 Years of Geodetic Surveys in Canada on the Government of Canada's website.
At the first stage of this two stage multi-cache you will find a monument known as a "fundamental benchmark". What looks like a small concrete block is actually a 7 foot monument burried under ground! The image below (from the Government of Canada website linked above) illustrates the true size. In case the top surface level bronze "tablet" got damaged, a second, backup version is safely stored underground.
Left: Schematic of fundamental benchmark. Right: Two technicians in the field using a fundamental benchmark to measure height differences
This survey marker was placed here in 1927 as far as I can tell from my research, just a few years after Gage Park officially became a park. On the bronze tablet the elevation above sea level is still printed in feet and, remarkably, it's to 3 decimal places that is millimeter level accuracy!
The elevation of this marker is written on the bronze tablet in the form ABC.XYZ
Final Stage Location:
N 43° 14.(250+ABC)' W 79° 49.(462+XYZ)'
Congratulations jtee on the FTW!