A big magnolia tree at the 18th Street edge of Dolores Park appears to have broken at its base and tumbled over onto the street, downing some power lines and impacting Muni bus service.

The tree across from Mission High School seems to have fallen of its own accord sometime after 8 a.m. on Saturday, and crews have now shut down the street as they remove it. One city worker whom Mission Local asked said the cause of the tree's demise was, simply, "gravity."

At 9:40 a.m., the SFMTA tweeted that the 33 bus line was being impacted by the fallen tree. And as ABC 7 reports, the tree took out a couple of electric lines that power that bus.

The tree is one of several magnolias that provide shade to the grassy area bordering the tennis courts and basketball court, and its absence is likely to be noticed.

The tree removal process is ongoing as of 10:45 a.m., as you can see below, and San Franciscans are being told to avoid the area.