The error is a result of how the code chunk was written.
I included an 'arrow' (i.e., --->) in my code chunks to help with organizing the document outline (see below). While this didn’t produce any issues for Knit in other chunks; the inclusion of the 'arrow' in a chunk with a plot command will consistently fail.
Solution Do not include an 'arrow' (i.e., --->) in any code chunks.
Example of original code chunk
> ```{r ---> McGill, eval=TRUE, echo=FALSE, message=FALSE }
>```
Revised code chunk
> ```{r McGill, eval=TRUE, echo=FALSE, message=FALSE }
>```