Find certain values of a csv file

I'm trying to discern the points of this attached csv file that have values less than -6000. I know booleans aren't really a thing on MATLAB, so I'm not sure how I can achieve this, especially given the size of the csv file. I need to figure out the points which have values of less than -6000 and then find the mean of those values, which I know how to do. I'm just stuck with the coding of how to set a range of acceptable values on this csv file.

Answer 1

[Walter Roberson]

t=load('mariana_depth - Copy.csv');
mean(t(t<-6000))