The former Tottenham and Liverpool striker hit the crossbar with his first-half spot-kick at Buck Shaw Stadium.
Bruce Arena's in-form Galaxy side took a 28th-minute lead thanks to Omar Gonzalez in Santa Clara.
But the hosts levelled just after the hour-mark through Chris Wondolowski to grab a point despite their winless run stretching to eight matches.
The Galaxy are on a seven-match unbeaten run and sit second in the Western Conference, three points behind leaders the Seattle Sounders.
Baggio Husidic went close in the 25th minute for the Galaxy as his scuffed 25-yard effort hit the post.
The visitors took the lead three minutes later as Gonzalez headed in Stefan Ishizaki's corner.
Jason Hernandez blocked a shot with his hand in the area to give the Galaxy a penalty soon after, but Keane's placed effort hit the bar.
It would be a miss the Galaxy would rue as Wondolowski levelled in the 65th minute.
Jordan Stewart's shot from the edge of the area found its way to the back post, where Wondolowski was on hand to scramble it in and earn the Earthquakes a point.
