then the rockfall occurred. it undermined the building. once the building was undermined, it could no longer state occupied, and the decision was made to remove the building. as you recall, it made headlines. eventually, the building was removed and a new wall was built. the lot where 22 once sat is still there. there are big disputes over whether it can be developed safely predict -- developed safely. and the filbert street stairs, because of the rockfall that occurred, new stairs were built, and they were built in a manner that when rockfalls occur, that actually lift out the stairs and put them on the ground and allow the crane to get back there to access the rockfall. >> beyond that, the building that we see at the bottom of the rockfall was actually designed to allow barack to fall off and be compounded by the building -- actually designed to allow barack to fall off and be impounded by the building. >> that is the corner of sansome and green. every couple years, there is a rock fall that occurs behind that building. >> now we are on

we are here to talk about rockslide, rockfalls, and related issues. what is the difference between a geologist and a geotechnical engineer? >> and engineering geologist deals with identifying site characteristics, mapping, the ground's surface, collecting all of this data. the engineer can come up with medications and designs. >> the structural engineer might be working on a building if there is a building involved. what is your role? >> i am interested in the physical properties of the earth and how the earth will behave: subject to different load changes. when you are building a building, you are applying a load and you are wondering if the earth will be able to supply that load. we work closely together and we come up with practical engineering solutions. >> this is when someone wants to build something. also, we have a rock piece of land. we have to have a resolution. >> in the u.s., about 2/3 of the population lives in areas that are prone to landslides. about $2 billion of damage occurs annually from landslides. unfortunately, 20-25 million peop

>> that particular building, if you look closely, the rock has actually receded back because of rockfalls. it was too expensive to put in foundations, so the foundation for that building is right on the surface. over the years, the rock face has receded to the point now where the flooding in the face of the bluff come together -- the footing and the face of the building and the bloc come together and are exposed. >> the confidence in the building is starting to be undermined. down at the bottom of the hill, out towards the bed, there are all kinds of uses there. what on earth would they be doing? >> what you are looking at here, two things occur along the south waterfront. one, sand that is dredged from the sacramento river is actually put on barges and brought down into the bag at pier 80 and 92, and then they stockpiled the sand and wash it and tip it over to the concrete producers, bodhi, central, and others, rose and jensen, hanson, and the sand is coming down the sacramento river to mix with the aggregate to make concrete. the other thing that happens down in this area of san francis