This is not a Challenger 600...it's a Gulfstream Global Express BD-700-1A10

Sorry bengleman, mboegler is correct, this is a Bombardier CL-600 and not a Global Express. The Global has almost twice the number of windows than this stubby little thing.
Gulfstream doesn't make Globals either, Bombardier does.
Looking up N numbers is so easy with reliable web sites like this one.
http://www.airport-data.com/aircraft/N121RS.html

Jim, thanks for providing the correction on this one. Has the "N" number registration changed on this aircraft? The FAA registry appears to show a different Bombardier.

It appears that the owner -- presumably Valero -- upgraded from a CL60 to a GLEX.

Conner, that V on the tail is actually for the company Vista Equity. I had initially thought Valero also when i first saw it,