Why this Earthcache is here
St Mary's Watershed is an interesting area in Southern Maryland. When you arrive at ground zero you will find a dam and a plaque. Take a good look around the water and you will need to make some observations in order to answer the questions. The plaque will only answer one question so you will not be able to research the rest of the answers off the internet. Our goal is to provide some history of the geology of this area, a lesson on how important this area is to Chesapeake Bay and to enjoy your trip.
WATERSHEDS
A watershed is the geographic area that contributes water runoff into a stream. How is this geologically important, you ask? A watershed, a.k.a. drainage basin, is the primary transportation system of water carried sediment. It also provides nutrients for vegetation and wildlife that live here, which may also affect the local geology. An example is rainstorms: When it rains, the water naturally flows downhill, until something blocks its path. This "something" can be land, vegetation, man-made structures, debris, and even more water.
This watershed is a flood control dam for the local area and protects thousands of acres. Situated at the northern end of the St. Mary's River, the park has a wide variety of habitats, from wooded acres and fields to swamps and small streams.
The St Mary's River is one of 150 rivers and streams that drain into the Chesapeake Bay. The Chesapeake Bay is the largest estuary in the United States. It lies off the Atlantic Ocean, surrounded by Maryland and Virginia. The Chesapeake Bay's drainage basin covers 64,299 square miles in the District of Columbia and parts of six states: New York, Pennsylvania, Delaware, Maryland, Virginia, and West Virginia. More than 150 rivers and streams drain into the bay.
The soil, sand and rock found in the ground acts as a filter or sponge for the rain and surface water. Contaminants from roads, oils, pesticides re mixed with the rain water and absorbed into the soil. As the contaminated water filters through the soil, sand and rocks, it purifies the water so that when it reaches the ground water (the underground rivers) it has less contaminates to pollute the rivers and lakes that it flows into.
Geology, Shape and Form
The basal skeleton of St. Mary County is built tip of unconsolidated strata, only Neocene formations being found in St. Mary. The materials composing these strata are the same as in Calvert County, even in respect to the marl beds. In the same way the later Pleistocene deposits are far more directly concerned in the formation of soil types than are the older strata, and the correlation of soil types with geological formations given in considerable detail for Calvert County also applies to St. Mary.
The chief geological difference between the two counties lies in the fact that in St. Mary the Eocene strata do not reach the surface, while in Calvert county they do, and the Nomini formation is much more widely developed in southern St. Mary than in Calvert county.
The area is made up of Susquehanna gravel and Sassafras sandy loam mixed in with Norfolk Loam.
Norfolk loam extends as a long narrow strip along the highest portion of the divide between the Patuxent River drainage and that of the Potomac River. It also occupies small, irregular, scattered areas covering the flat plateau of the northern portion of the county.
Along the Three Notch Road, which follows the main divide of the county, the area occupied by the Norfolk loam presents a slightly rolling upland, vaiying from 120 to 165 feet in elevation. The highest elevations and the intervening hollows are included in the area covered by this soil.
The soil itself consists of a fine sandy to silty loam, reaching to an average depth of about 1 foot. When dry it is powdery and loose, resembling corn meal in texture, distinctly lacking the smooth, clayey feeling of the finer-grained Leonardtown loam. When wet it packs to a firm surface, which cakes slightly through sun drying. In plowed fields this soil, though distinctly sandy, may clod into large-sized lumps. The subsoil is a reddish yellow sandy loam, finer in texture than the surface soil. It extends to a depth of about 30 inches and is almost universally underlaid by a coarse red sand mixed with fine gravel, having an indefinite depth.
The soil supports a natural growth of pitch pine, white oak and black oak, and chestnut, this latter tree occurring more frequently on this soil than on any other type represented in the county. The areas of Norfolk loam occurring in the northern portion of St. Mary County, particularly in the vicinity of St. Joseph's Church, constitute what is locally recognized as one of the most desirable tobacco soils in the county. The average yield per acre is about 1,300 pounds, and the average price about G cents per pound. Wheat, corn, and clover are also raised on this soil in regular rotation with the staple tobacco crop. The yield of these crops on the Norfolk loam compares favorably with the average yield of the same crops over the entire area of the county.
If you are with a group of people, only one person needs to send in answers, just ensure you list all the names in the group.
Please follow your GPS to the posted coordinates to find an excellent information plaque regarding this location.
QUESTIONS
To receive credit for this Earth Cache, answer these questions in an email to the cache owner. Please do not post the answers in your online log.
1. What kind of strata does not reach the surface in St Mary's County but does in Calvert County?
2. Norfolk Loam is mixed with what in this area?
3. What is the Floodwater Retarding Storage (Acre feet) of this dam?
4. What is your estimate of the height of the dam, from the base to the top. Why do you think it is so high?
5. Walking along the dam. On the west side what color is the sand and rocks ?
6. This watershed is used as a filter for the Chesapeake Bay, in your opinion how does the geology of this area accomplish this ?
7. Optional Photo: Post a picture from the top of the levee, looking north doing something goofy.
Citation:
BONSTEEL, J. A. (1901, June). The soils of St. Mary's County, MD.
Retrieved from http://www27.us.archive.org/stream/soilsofstmarysco01bons/soilsofstmarysco01bons_djvu.txt