Notes on the Potomac Forks

Reference in C&O Canal Companion:
Historical Sketch, p. 6-7 and Canal Guide Mile 164.8

This USGS aerial photograph shows the relative sizes
of the North and South Branches of the Potomac
at their juncture just below Oldtown, Maryland.
(United States Geological Survey)


from Governor Sharpe's letter to Lord Calvert, September 14. 1753 (page 5, Volume 6, Archives of Maryland).

Mr Cressop gave it as his Opinion to the Council that the Temporary Line is to the Northwd of any Bendings of the River Potomack & that the South Branch runs 60 or 80 Miles farther West then the Spring Head of the Northern Branch upon wch representation of His by Advice of the Council I have wrote the following Lettr to Ld Fairfax.


[Sharpe to Lord Fairfax.] My Lord I have the honour of acquainting your Lordship with my appointment to this Government and at the same time expressing Sincere Satisfaction from the hopes of being instrumental in forwarding a mutual Benefit to your Lordship as well as the Lord Proprietary of this Province Lord Baltimore was pleased to Charge me with an Enquiry into the True Meridian and Place of the Fountain head of Patowmeck; The best Information I have been hitherto able to procure gives me Reason to believe there has been a mistake in fixing the Spring head to the North Branch since the Length with other Circumstances more properly denotes the Southern Branch commonly called Wappacomo to be the main & principal Course of that River. I am the more willing to be persuaded of the Truth of this Representation from the considerable Advantage that will accrue to your Lordship. That Branch I am Informed has never been thoroughly explored and traced to it's Source, but I flatter myself with having your Lordship's Concurrance for such an Examination into its Course Length Width and Depth as may bring this Matter to a nearer degree of Certainty and if that should appear to be the fountain head of Patowmeck River I shall not Question but your Lordship will be for taking such measures as may ascertain the mutual Limits of the two Proprietorships Agreeable to the Direction and True Intention of their Respective Charters.

from Governor Sharpe's letter to Lord Calvert, November 29. 1753 (page 14, Volume 6, Archives of Maryland).

My intent to examine the two Branches of Potowmack I have hinted to the Govr of Virginia & writ to Colo Cressop to know whether He will undertake that Business or not, & re- turn me an accurate Description of their Courses, Rapidity & Depth & the longitudinal Difference of the places of the Spring Heads, but I suppose the severity of the Winter will hinder Him from proceeding on those Enquiries this three or four Months at least.

from Lord Calvert to Governor Sharpe, April 17th, 1754 (pages 44ff, Volume 6, Archives of Maryland)

By Lord Fairfax's Letter to you, his Lordship Declines having to Do with any Re-Settlement of the Course of Potomack River. The Branch called the South Branch which you seem to apprehend will be much more Beneficial to Maryland, as in Length South Westward, will depend on Proof, as it's Fountain Head instead of the Spring Head of the said River, determined by the Virginia Commissioners in 1736 and 1737. If the South Branch runs as you apprehend, it will certainly be of great Advantage to the Encrease of Maryland, and also may be to Lord Fairfax's Tract of Land by the Spring head of Potomack lying more Westward than the Determin'd Head of Potomack as above settled. However you ought before you make an Attempt, to be well Grounded How the Inclinations of the Governor, the Virginians and Lord Fairfax Stand, to a New Settlement of the Course and Fountain of Potomack with Maryland. If they oppose, the Crown is most likely will side with Them. The Tryal of the South Branch of Potomack as to it's advantages as may turn out, His Lordship is not against Mr Cressap's Essay therein ; Provided he does not bring upon Him too great Cost thereby, of which, if you find it absolutely necessary to send him; you must Bargain with him Reasonably.

from Governor Sharpe's letter to Lord Calvert, June 6, 1754 (pages 70-72, Volume 6, Archives of Maryland).

... It is owing to Colo Cressap's Absence from home among the Virginians on Ohio, that I am not yet able to comply with your Requisition concerning the Latitude of the most northern Bend of Potomack I some weeks since writ two Letters desiring him to return me a Copy of his Map of that River signed & authenticated which I will transmit with the Description of Distances & Bearings of the River Heads on the Eastern Shore as soon as the Surveyors make their Returns which I expect in about 3 weeks or a month at farthest ...


P. S. I have this Instant received a Letter from Colo Cresap with the Plan & Certificate concerning the North Branch of Potowmack & the Temporary Line as run by him.

Facsimile of Cresap's Map:

From Charles Fenton Mercer's December 1832
reports to the Directors of the Canal Company:

Let the next dam, No. 7, be erected in like manner, immediately below the South Branch of the Potomac, and a Canal, twenty-five miles in length, be conducted from thence, to the highest point, on the pond of still water, behind dam No. 6, whence a navigation for the Canal boats, or six feet depth of water, can be had down to the dam. The dam, at the mouth of the South Branch, will cause a still water navigation to extend as far up the Potomac as above Alum Hill, a distance of three miles.

* Alum Hill is at Oldtown. This 1832 proposal was based on the use of stillwater navigation behind Dams 4-8, but promised that this would be a temporary expedient. Dam #7, which was initially intended to be built just below Potomac Forks, was never constructed.



  • Sharpe/Calvert correspondence is from Volume 6 of the Archives of Maryland, Correspondence of Governor Horatio Sharpe, Volume I, 1753-57, William Hand Browne, Maryland Historical Society, Baltimore, 1895. [On-line at Maryland State Archives]
  • Facsimile of Cresap's map of the South Branch from Library of Congress, Maps and Geography Division. [The facsimilie appears in Archives of Maryland, Volume 6, Correspondence of Governor Horatio Sharpe, on-line at Maryland State Archives -- the location of the original map is not indicated.]
  • "Two Reports of the President to the Directors of the Chesapeake and Ohio Canal Company on the Present State of the Finances of the Company, and an Extension of the Navigation of the Potomac to a Point Nine Miles Above the Town of Cumberland," signed by C.F. Mercer, December 15, 1832, printed by Gales and Seaton, Washington, DC, 1832.

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