We encounter all sorts of mundane mysteries on a nearly daily basis in Los Angeles. Why is that helicopter hovering over Koreatown? What's really in In-N-Out's secret "spread" recipe? Why is there traffic on the 101 at 2am?
While we can't always answer those (though we're pretty sure the "spread" is just Thousand Island dressing), we can solve this question: Why are there bumpy, ugly square plates stuck to the side of so many old buildings in LA?
The short answer: earthquakes. Los Angeles is full of old (and cheap) brick and concrete buildings, oftentimes ones that were built without any sort of load-bearing reinforcement. To remedy this, most of these old buildings were fitted with bolts that secured the exterior walls to other building structures like ceilings. The majority of those bolts are hidden inside of the walls, except for one part that's visible from the exterior: those ugly wooden and metal diamonds, which are actually called anchor plates or wall washers.
Anchor bolts were added to local building codes in the late 1930s, according to the LA Times, and were considered adequate seismic safety for another 50 years—until we realized that wasn't enough and moved on to more modern engineering standards. Hence, you won't find anchor plates on any contemporary buildings.
That explains why they're there, but why are they often so unsightly? Chalk that up to a lack of money or taste—for every beautiful building there are a dozen ugly ones. Some building owners chose to stucco over them, effectively hiding the bolts, but plenty of others seem unconcerned with having dull diamonds mar the facade. On the other hand, here's what you can turn those into with a little bit of money and good design:
Photograph: Carl Manzi/Wikimedia
Photograph: Frank Vincentz/Wikimedia
Photograph: Etan J. Tal/Wikimedia