Actually, I haven’t made much effort to do this, but here are some ways to start…
Use the link at right to Maryland Inventory of Historic Properties, where you can search by name, browse within counties, and so forth.
- Magruder sites include Anchovie Hills and Dunblane. Most of the early Magruder plantations were in what is now Prince George’s County.
- Magruder’s Landing (now Magruder’s Ferry) can easily be found on the map, as it’s now a park and public boat launch. Anchovie Hills was/is just uphill from there. When I tried to find in about a dozen years ago, the property was overgrown and going unused.
- Descriptions of the properties were current when application was first made for historic protection, so check the date on the documents, and browse for other information, like where the original surveys and deeds may be found.
- I have had the best luck searching with a “Begins with” string, rather than trying to match the exact name they have in the database.
In her 1959 book, Prince George’s County Heritage, Louise Joyner Heinton included a fold-out map of tracts as they were laid out in the early years of the county. There little correlation to modern landmarks, but major watercourses and the rail line give some aid. The early Magruder properties were all in the portion that had been Calvert County before P.G. was founded. The original of this map should be at the Maryland Hall of Records, according to a note in the book.
- I used this map as I drove around the area back in the 90s, and was able to locate some properties, at least approximately. It helps when developers name streets for the old plantations.
- Alexander’s plantations Anchovie Hills, Good Luck, Alexandria, Craignecht, and Dunblane all appear on this map.
Use the link at right to Find a Grave. Family cemeteries are one way to locate a vanished home site. Several significant Magruder cemeteries in Prince George’s County.
Oakley Cabin African American Museum, Olney, MD (Montgomery County). Oakley Farm was purchased by Dr. William Bowie Magruder in 1836. Lots of interesting sites near-by.
Magruder's Landing 
I remember reading in some document a description of a Magruder and his daughter on horseback; the father pointing to a hillside saying, “That is where the original Magruder – Alexander – lived and was buried.” Wish I’d kept the link to that source. I’d love to drive around there and search for the original homesites. The graves are likely unmarked at this point.
Ah! That’s Alice Maude Ewell’s memoir about her grandmother Ellen McGregor Ewell. You probably read the excerpt published in the ACGS Yearbook. Click the link at right for American Clan Gregor Society Yearbooks, and find the one for 1918. (One advantage of working on this site is that I had to pull together all the stuff I’ve read, so for once I actually know where most things are.)
That should say “find the one for 1914.” The Ewell excerpt starts on p39. On p42, she attributes her grandmother’s fortitude during the Civil War to inherited memories of hiding in caves to survive persecution during the Clan Gregor proscription–exactly the kind of thing that makes me say that by the 19th c. the American Magruders didn’t know anything about Alexander’s actual life.
I have a copy of the Louise Joyner Hienton map of tracts laid out in Calvert County prior to 1696. Both the recorded dates and locations of the Alexander Magruder tracts are of interest.
Apr 2 1666 Anchovies Hills (near Magruders Landing).
May 15 1670 Good Luck
May 28 1670. Alexandria
Jun 26 1671 Craigneich and Dunblane (all four surround Upper Marlboro).
All these dates seem to me to be the actual dates of Alex acquiring land, the earlier 1650 era dates being merely him being given a head right or paper option.
Ninian Magruder acquired Beall’s Gift in 1695, which is located near Glenn Dale/Hillmeade
I have that map, too. What I never had time to do was to drive around Maryland to fine these (& the many later Magruder farms), or what is left of them. My own family’s last farm-site is now an industrial park, though I’m told if you find the right person to ask you can still get in to see the family burial plot.