Welcome to the wonderful world of olive oil. Olive oil is similar to wine with regards to soil type/climate/varieties/extent of maturation at time of harvest. Different soil types can emit different characteristics of the variety of olive that is being grown which goes in hand with the climatic region. Recently, an Italian friend of mine remarked that the oil we produced from my area was very similar in viscosity to the oil produced in his native Puglia. Umberto thought the oils from northern Italy and France were "too thin". Indeed, our latitudes are pretty close, but I haven't checked the Puglian soil types!
There are hundreds of olive varieties. The most common varieties are from Spain and Italy, but there are varieties indigenous to almost every olive growing region in the world. There are not specific green and black olive varieties as many people assume. Olives are green until they ripen, and then they turn black/dark purple. This is the one area in which the grower has the most control over the final olive oil taste profile. The greener the olives are picked, the more grassy and green the oil will be. The more mature the olive, the milder and more yellow/golden the oil will be. In addition, there are different varieties of olives that lend themselves more to one taste profile than another. Recent trends in California olive oil production seem to lean towards the bolder, more robust green type olive oil.
More to come....