The National League West is right now a 3-way tie among San Diego, Los Angeles, and Colorado. The teams are all 44-40.
The other second place teams in the NL are Cincinnati (44-41) and Philadelphia (38-45). So right now, the wildcard would come from the West.
But who would it be? How would this be determined? If there are two teams tied for first and both would make the playoffs, then the team with the edge in the season series gets the division title as was the case in 2005 with the Yankees and Red Sox in the AL East.
However, you couldn't do this in the NL West as there is no provision for a team to miss the postseason because of a tiebreaker.
My guess is that in the unlikely case of such a tie occurring at the end of the year, the three team playoff method would be held. The teams are seeded by their records against the other two teams. Presently that would be
Los Angeles, 10-7
San Diego, 9-8
So, first Colorado would play at San Diego. The winner of that game would then host Los Angeles to decide the division winner. Presumably then, the loser of the second game would play the loser of the first game to determine the wildcard.