This wonderful old image from the 1860s shows F St. near the end of the Civil War. The details are quite incredible when you click on the photo. I’m a little confused as to where this is exactly. The building in the background could be either the old patent office of the post office. But, the columns in the photo are Ionic, whereas the column on the old post office are Corinthian and those on the patent office are Doric.

Source: New York Public Library
Are these the columns of Treasury along 15th?
Why do you say this is F Street? There is a sign for a business with the name of Kendig. I looked him up in the 1865 tax records Martin N H Kendig Pawn broker business is at 214 Pennsylvania Avenue. On a Civil War era historic map it shows that this address is at the base of the Capitol Building. I don’t know if this photo was mislabeled or possibly Kendig had two locations. If this is 214 Pennsylvania Avenue it certainly would be an important photo. Thank you for finding it and posting.
Interesting, I found and 1863 paper that does have a Mr. M.H. Kendig doing business on F street as a notary but no address was given (http://chroniclingamerica.loc.gov/lccn/sn83045462/1863-09-01/ed-1/seq-2/).
The 1863 city directory doesn’t list him at all but the 1864 lists his business address as 217 F North “attorney for collection of claims”
I think luckybiker is right, F at 15th has a similar angle on the Treasury Building, which has Ionic columns: https://www.google.com/maps/@38.897349,-77.0331486,3a,75y,230.84h,83.99t/data=!3m6!1e1!3m4!1s8ZcOBcOMC_KrRb3Iefw9og!2e0!7i13312!8i6656!6m1!1e1
I also found a map from 1862 (http://hdl.loc.gov/loc.gmd/g3850.wd000565)
that has a hospital and a jail in one large block that covers the blocks
bounded by E and F between 4th and 5th and either may be
what is in the background depending on the direction that one is looking
toward. Looking at the 1864 directory I couldn’t match a hospital but the county
jail was at the corner of 4th west and G north.
It’s definitely F Street looking west to 15th Street, NW, and Robert Mills’ east wing of the Treasury. The F Street buildings are great — the one on the corner qualifies as Greek revival, while the two late Federal style houses w/ the arched ground floor windows are extremely elegant. One curiosity: note the very steep rooflines. The two houses at left are consistent Federal vernacular, although the doorways look Greekish.
The more I look the more I agree – that does look like the Treasury Building from the columns to the shorter retaining wall that is still there where F dead ends.
Does anyone know if the building numbering system changed for DC? I find it odd that he is on F but current numbering puts him closer to the Capitol. I doubt he had 2 locations on the same street that seems a bit odd. The 1865 directory still has Kendig on F at 215 but also at 256 G N.
The columns look like 911 F, what is currently Ultra Bar, although the other buildings don’t seem to match up.
House numbers changed post-Civil War–described here: https://matthewbgilmore.wordpress.com/house-history/ The present system of numbering the houses (buildings) in Washington City was devised by E. Dwight Clapp and was adopted by the Aldermen and Common Council of Washington on November 29, 1869.
To confirm what a few others had posted below, it is 100% F looking across 15th to Treasury. I work two blocks away, and just went to have a look. Everything completely lines up from the Treasury east side, including the bit you can just see around the corner where a double column begins to bump out toward 15th. Also, the column work is definitely not the patent building/portrait gallery. I went there too, and the decoration is just wrong. It was difficult not to believe initially it was F at the patent building, since the remaining building on the NW corner of F and 9th (the one that says “Masonic” on it) looks suspiciously like it could have been a combination and expansion/redecoration of the last two buildings on the right just before the intersection. But it’s definitely f and 15th. Too bad the Hotel Washington and Willard have now obliterated those cool old buildings…
It looks like it’s looking east at 9th st. and those columns belong to the Patent Office.
1434 F st. NW.
https://www.google.com/maps/@38.8973767,-77.0331878,3a,47.5y,246.81h,93.52t/data=!3m6!1e1!3m4!1sqD1ujiQBLv5GnbNLFa9nTw!2e0!7i13312!8i6656