[R] Extraneous full stop in csv read

[John]

I ran into a puzzling minor behaviour I would like to understand.
Reading in a csv file, I find an extraneous "." after a column header,
"in" [short for "inches"] thus, "in.". Is this due to "in" being
reserved?  I initially blamed this on RStudio or to processing the data
through LibreCalc. However, the same result occurs in a console R
session.  Sending the file to the console via less reveals no strange
characters in the first line.  The data is California statewide
rainfall which was screen captured from the Western Regional Climate
Center web site.

First 15 lines including header line:

"yr","mo","Data","in"
1895,1,8243,8.243
1895,2,2265,2.265
1895,3,2340,2.34
1895,4,1014,1.014
1895,5,1281,1.281
1895,6,58,0.058
1895,7,156,0.156
1895,8,140,0.14
1895,9,1087,1.087
1895,10,322,0.322
1895,11,1331,1.331
1895,12,2428,2.428
1896,1,7156,7.156
1896,2,712,0.712
1896,3,2982,2.982

File read in as follows:

x <- read.csv('DRI-mo-prp.csv', header = T)

Structure:

 str(x)
'data.frame':   1469 obs. of  4 variables:
 $ yr  : int  1895 1895 1895 1895 1895 1895 1895 1895 1895 1895 ...
 $ mo  : int  1 2 3 4 5 6 7 8 9 10 ...
 $ Data: int  8243 2265 2340 1014 1281 58 156 140 1087 322 ...
 $ in. : num  8.24 2.27 2.34 1.01 1.28 ...
[note "in" is now "in."]