Thank you all very much for your comments!
Thank you, Mike, for the clean-up, it is wonderful! Having the creases removed draws my eyes to Patrick and the horse - before the clean-up I was distracted by the marks.
Jim, I was thinking it might be around 1910. If it was c1905-1910, it could have been just before the devastating earthquake. It's something for me to think about. (I feel like there is a clue, somewhere.)
Patrick was Roman Catholic and I believe religion was a part of his life.
Thank you for the link, Mike; I will read it after posting this.
Pennant lance support - very good suggestion.
Street cars: I am not sure what he did. I will research that. (I know that he was a "Driver" at some point, but I don't believe it was meant in the literal way.)
Address on the back of the photo: Patrick is my husband's ancestor. Now that I am communicating with his cousins and we are sharing information and photographs, I have seen a number of photographs for this family. Addresses have been included on some of the photos, possibly because the family changed locations several times (due in part to the 1906 earthquake). Supposedly, Patrick helped his son-in-law build/update (an "earthquake shack") their residence after 1906. However, looking at the writing on the back, it is fairly large - scrawled across the back. That is not consistent with how the addresses were written on other photos. I will look for a sample of his writing, to see if it could be Patrick's writing or possibly a photographer's writing.
Writing on the building: The abbreviations for the railway were (I thought) odd ones. I will research the abbrevations again.
My mother-in-law only mentioned a few things about Patrick - one was that he used to tell her to sit up straight. (He must have told her that a lot, for her to comment about it.)
I met one of his granddaughters; she had a deep love for Ireland - perhaps acquired from Patrick? The cousin who just shared this photo with me said that she had heard of Patrick's "fierce love" for Ireland. She feels that the photo is of Patrick being in a parade; possibly for the Hibernian society. She also said a family member has a photograph of Patrick - there are a lot of people in the photograph - perhaps members of a society.
Thank you all very much for your thoughts; we have a lot to research and think about. Mike, thank you again for the touch up. Now that I've replied, additional comments most welcomed about my reply or any other ideas. Thank you, Lisa