under like 1km or more there is still magma .
I doubt it. The core of mars has run out of fissile materials and has stopped rotating. So I'm not sure why you would expect magma near the surface when the hottest part of Mars' insides has gone cold.
We know this because there isn't a magnetic field, if the core was molten then there would still be one. But there isn't.
Yup, on Earth the magma is generally found at least 2 km under the surface in volcanic places. On Mars I expect we'd have to dig though at least 1/3 of the crust, or about 10 km, before we even get geothermal warmth.
Then again, we can still land on Olympus Mons, for 4 good reasons:
1. Proclaim ourselves Gods
2. Landing on the biggest volcano
3. Underground glacier for ice and water
4. It's close to the equator, making taking off easier.
We can also abuse the fact that the top sticks out of the athmosphere for an observationall centrum, and we shouldn't have much problem with dust storms when we get high enough. Problem is that the higher we go the more dangerous solar radiation becomes, and the harder landing becomes.
EDIT: Actually, Olympus Mons Is a bad location. It stands in one of the dustied places on Mars.
PS: Fun fact, Olympus Mons is so large you can't see the entire thing from the surface. It dissapears over the horizon. So when you stand on the top, you don't even notice it.