Alameda Seniors Mastick Center to browse and sign-up for exercise/computers/art/discussion groups. Also on Bay Farm Island there are various club associations along with your HOA.
Interested in locating property to buy? I can help you, having lived here for several decades. Cell 510.289.3737. Jennie Wong, BHG Realtor http://www.bhghome.com/JennieWong/mylinks/aspx
Yes, as others have said, Alameda is a very friendly place. You mentioned that you have a dog so walking your dog along the beach front will certainly bring you new acquaintences as will a visit to the dog park.
If you like to get out on the water (Alameda is an island after all) there are rowing and paddling clubs such as the Alameda Dragonflyers, a paddling group with members of all ages and ethnicities. In fact, they refer to themselves as a social club with a paddling problem~
If you like gardening there is a group called the Alameda Backyard Growers who meet up to share information and produce from their backyard gardens and their motto is "grow some, eat some, and give some away -- to the food bank. They donate their excess produce to the food bank for those in need. You don't even have to have a garden to be part of the group. If you like to garden, but don't have a plot of your own, there is always someone who would appreciate your help in their garden.
So there you have it. All kinds of possibilities for you to make new friends. I'm sure it won't take long. Feel free to be in touch if you would like to know more about any of these groups.
Here's an article about how it came about http://www.alamedamagazine.com/Alameda-Magazine/March-April-
And here's where you can see what event(s) are planned
Happily, Alameda offers so many activities ---- if you like to dance, check out Friday night Zydeco dancing class at Eagles (on Alameda Avenue, cross street Park St) http://www.sfzydeco.com/Eagles/eagles.htm You don't need to have a partner just to go. Learn the basic steps first, and then it's dancing all night. Folks ask other folks to dance.
Try that first.
Or if you want to see what seniors do for fun, try Mastick Center http://mastickcenter.com/ They offer a lot of activities as well.
Let me know what kinds of activities you're interested in, and I may be able to help.
Welcome to our beautiful island city :)