Your first element is a zero. Should that be included in the output? So you just want the last non-zero number in a stretch of non-zero numbers before it turns into a 0, right? Try this:
m = [0 0 0 0 30 60 90 120 119 118 2 1 0 0 0 3 4 0] % Create sample data.
dm = diff(m~=0) % Threshold and find element-to-element differences.
lastElements = find(dm == -1) % Find the indexes where it goes to zero.
