Like other workplaces, the bell tower needs to comply with OSHA noise standards.  Ear muffs hanging on the wall. 

Then he pulled ropes and bells sounded.  The person he was planning to train never showed up. 

Instead, the bell ringer decided to kill time by talking with me.  We discussed San Luis Obispo's confusing, in his opinion, building codes.  The mounds of paperwork required just to change a bell.  Old bells could be damaged, if used too much.  Newer ones are soon to be "swapped in" so the older ones can have their rest at the mission museum. 

Original part of mission dates back to late 1700s, but much was added later.  Bell tower may have been from early 1800s vintage. 
 
 

My 2004 Bike Tour

Some covered walkways, around outside, date to recent times, like 1950s? 

At one time, the church was covered in wood siding.  Tried to look a bit New England style.  Since then, siding has been removed and original adobe restored.  Most of the adobe is still protected with concrete surface.  Looks like it is reinforced with chicken wire.  Looks okay from outside.  Just a white adobe wall, but a bit more weather resistant than mud brick material inside the wall. 

Mission at San Luis Obispo is still a working parish.  Not just a museum frozen in time, but they strive to maintain much of the original character.