Datum conversion?

[+JohnCNA]

I'm working on a puzzle cache where the cache page clue is  a small area clip of an old USGS topo map with a circle on it to signify the search area.

 

So I found a 1954 topo map on the USGS web site that perfectly matches the picture on the cache page.

 

I did an overlay in Google earth and got some coordinates.  I also have 'ILTopo11' from GPSFileDepot installed on my Garmin and in Basecamp and can verify the search spot there, too.  We looked quite a while but did not find anything.  We didn't realize at the time that the target circle was around 250' in diameter and it is pretty difficult terrain, so we didn't widen our search radius that wide.  Before we try again, I thought I'd verify my previous sleuthing.

 

It turns out that the PDF map I downloaded from USGS is a 'GeoPDF' so I opened it into the free Adobe reader and hovered my mouse over the selected spot and the coordinates in the GeoPDF are around 750 feet away from my geocoded coordinates and the coordinates in Garmin or Basecamp.

 

So my question is....  Could they have been using a different Datum in 1954 than WGS84 that would account for the difference?  I've looked online at several coordinate converters but haven't found anything promising.

 

Edited July 21, 2021 by JohnCNA
Remove potential spoiler

[Moun10Bike]

WGS84 was developed in 1984, so they most assuredly were using a different datum - most likely NAD27.

[+JohnCNA]

Ah, thanks!  I found an online converter that would convert from one datum to another. Converting from NAD27 to WGS84 puts my 'bogus' 1954 PDF coordinates within a few feet of my present day geocoding with Google Earth. 

 

Now to convince my caching buddy to take that longish hike in 90° weather again.  😁