There are seven missions which consist primarily of using quarry machines to accomplish different tasks.
Thanks to www.gta-sanandreas.com for the mission walkthroughs
Mission 1: Use the bulldozer to clear the paths before the next delivery arrives. This mission is timed and requires you to push 7 rocks with the bulldozer into red marked areas in order to clear the path. This is relatively easy, although you'll use up most of your time driving around the quarry. Jump in the Dozer and drive forward. Drive into the rock and push it over the side, then head down to the right and push that rock over the side. Keep going around to the right and you'll notice the next rock is below you. Jump off the side and use the directions on the analog stick to keep the Dozer on it's wheels. Push the next rock off and head towards the next one which is to the left. You may have to drop down and go up the small ramp from the bottom level and to the left. Once you've got that, head back along the path and knock the next one off the road. Head up the path to the left and knock the next lower one down, then head along the path, up and to the left and knock the final rock off the end.
Mission 2: Bombs have been planted by a rival organization. Use the bulldozer to push the bombs to safe area markers. Again, this mission is timed, and again you need to push items around using the bulldozer. Get in the Dozer and you'll be told of a bomb behind the hut where you start the mission, so drive around to it and use the ramp at the front to push the barrel into the red circle. This can be pretty frustrating as the barrel doesn't exactly stick to the front of the vehicle, but you have more than enough time to do it. Once it's in you'll be told that there's a bomb at the crane so head down the hill (jump if you wish) and get behind the barrel and push it up the two slopes into the red circle. Rather easy that one. After that, drop down to the bottom of the Quarry where you'll need to push another barrel into a close red circle. It's not too difficult providing you approach it from directly behind. The next bomb is close again, just in between the crushers behind you. Push that into the red circle within the generous allotted time. Once it's pushed into the circle, get out of the truck and run like hell as it blows up.
Mission 3: The bombers are escaping in a dumper. Use this dumper to destroy it before they reach their destination. Another timed mission, although this one isn't as repetitive as before. Jump in the huge Dumper and make your way around the outside of the Quarry while chasing after the red blip on the radar. If you have a sub machine gun you can just drive by the truck until it goes boom. If not, do it the more fun way and try to blow it up by smashing into it, or even knock it into the water as it passes by through Tierra Robada. Once it's gone it's mission complete.
Mission 4: The bombers have been caught. Their bodies are loaded on a dumper at the quarry's other entrance. Dump them before the cops come snooping. You'll never guess that this is another timed mission too. Anyway, grab the Sanchez and make your way towards the blue blip on the radar at the other side of the quarry. Go around it, not through it. When you get there, get in the Dumper and follow the same route back to the Quarry Entrance. Be careful not to crash the Dumper though, as the bodies in the back aren't very stable and if they fall out it's a mission failure. Once you get back to the quarry entrance, follow the path down to the left and reverse towards the fire when you reach it. Pull back on the right analog stick and the dumper will tip out the bodies onto the fire.
Mission 5: The dumper is loaded with explosives and needs to be driven gently. Deliver the explosives to the desert airstrip. This mission is once again timed, but you also need to ensure you drive carefully as one hard impact or about three soft ones will cause the barrels to explode. Choose your own route to the desert airstrip, the best way is to go to the right, follow the road along and to the left and then North and left again and work your way down to the drop off point. In some game versions a glitch occurs on this mission and the game will award you a huge insane stunt bonus when you drop the barrels in the red circle - free money.
Mission 6: A dumper has spilled it's load of explosives along the train tracks. Use the bulldozer to clear them before the next train passes. It's timed again. Get in the bulldozer and make your way towards the train tracks which you'll find by going straight forward and then left and down onto the tracks. From there just drive along the tracks and push all of the barrels with green arrows off the side until the arrow disappears. Keep going along and remove them all before the time runs out. Relatively simple, compared to the mission difficulty progress that happens in the other missions.
Mission 7: A cop has been killed. Use the bulldozer in the quarry to get rid of the body before more cops come snooping. Grab the Sanchez and use it to jump all of the way to the bottom of the quarry. Once there, get in the Dozer and you'll be told to push the body and bike towards the crane pick up area. Head to the right and get behind the body, then push it down the hill towards the crane. Leave it in the red circle then head across the other side of the area and push the bike towards the same place. Once it's there, grab your Sanchez if you parked it close and drive up the hill to the crane. Once there, stand in the red circle and push triangle to get in the crane. Spin it around to the left and hold X and manoeuvre the crane to pick up both the body and bike, then hold square to lift up the crane and drop them one by one into the back of the dumper. Once they're in you'll be told to get into the Dumper and drive to the Quarry Entrance. Carefully make your way up the hill and drive through the gates. From here you'll be told to dump the body and bike into the water. Head to the red circle and reverse up to the water. Pull back on the analog stick to dump the objects into the water.
Reward: $10,000 All Quarry Missions have been completed. Hunter Quarry has now been Acquired as an Asset. The dumper truck and bulldozer will now always be available at the quarry.