High Park shares a common geological history with the rest of the waterfront areas of the Toronto Region. Canadian Shield bedrock is situated about 400 metres below the surface. Sitting on top of this are a number of layers formed at various times over geological history starting with limestone formed when the area was an ancient sea. Over the past 135,000 years, though a series of glacial advances and retreats, additional levels were laid down. The most recent glaciation, which began its withdrawal down the St Lawrence River valley about 12,500 years ago, set the stage for the creation of Lake Iroquois, a large lake covering the present Lake Ontario basin. The lake was formed from melt water from the glaciers. Because the ice blocked the present St Lawrence River, the melt water from Lake Iroquois flowed south to the Hudson River in what is now upper New York State.
Lake Iroquois was much deeper than present day Lake Ontario. High Park would have been under sixty metres of water. During this period, large deposits of sand and other fine material were laid down under water over the present shoreline and High Park.
About 12,200 years ago, the St Lawrence Valley where Kingston is today, suddenly opened, and the water from Lake Iroquois quickly drained. Two factors exacerbated the extent of the drainage. First, the land in the St. Lawrence area was depressed by the weight of the glaciers, compared to current levels, meaning drainage was more rapid. Second, the ocean was about 100 metres below current levels, as much sea water was tied up in glaciers. This lower level meant that more water could leave the basin compared to now. The situation was like a tilted bathtub with a drain in the St. Lawrence meaning that the resulting new lake shoreline was about 8 kilometres south of High Park. Rivers and streams that drained into Lake Iroquois now flowed offshore and immediately began to cut into the soft sandy sediments that were formally lake bottom.
In High Park, water flowing through Spring Creek and Wendigo Creek cut deep steep sided ravines in the Park. Spring Creek entered the current Park at Parkside Avenue and Bloor Street and meandered southerly. Spring Creek had a number of tributaries that can be clearly seen such as the ravine where the adventure playground is located and the ravine where the zoo is located. A number of smaller ravines fed into these and the Creek. These ravines and streams accounted for 50% of the Park area. They contained forest vegetation. The land left between the ravines, termed tablelands, was sandy and relatively warm. This land supported more southerly plant types including Black Oak forests and open areas or savannahs with a prairie under story. (oak savannahs are considered a provincially rare community type). The valley bottoms and slopes were swampy and cooler and supported more northerly species such as cedar, red oak and other such plants.
Further geological changes took place that affects High Park. The land at the eastern end of Lake Ontario began to rise after the ice had retreated and the weight of the ice was removed. This rising of the land reduced the flow from the Lake and caused lake levels to rise. Over the time, the lake levels continued rising and the shoreline moved to its current location. When this happened, the valleys of the streams, that had cut into the soft sediments and flowed out to Lake Iroquois, were flooded. The wave action of the present day beaches and resulting sediment movement eventually blocked the mouth of the Creeks trapping ponds behind them. This is the origin of Grenadier Pond on Wendigo Creek and the marshy area at the lower part of Spring Creek. Grenadier Pond is the City of Toronto's only remaining lakeshore marsh and occupies most of the western side of the park.
John Howard's Plan of Survey, High Park 1864
The shores of the precursors to Lake Ontario
To prove you came to the coordinates and learned a geoscience lesson answer the following questions:
Look at the vegetation around the posted coordinates:
1. What geological changes over time do you think made it easier for the most common trees you see in the area to grow than another species?
2. Would you the land around GZ is flat or hilly?
2b. Why is the land in this form and what caused it to be like this?
3. Take a soil sample and/or examine the soil profile. Describe what you see. Which of the six main types of soil if your same most like and why?
- Clay
- Sandy
- Silty
- Peaty
- Chalky
- Loamy
4. Optional: Take of picture of you or your GPS/Phone at GZ to prove you were there. (Including Grenadier pond or the marshes if possible)