Just a suggestion based on the context provided.

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Note added at 1 day1 hr (2008-09-22 12:15:24 GMT)
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In full:

detailed measurement of / pinpointing the location in / application of predetermined reference positions to

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Note added at 1 day9 hrs (2008-09-22 19:48:36 GMT)
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Here is a full list of meanings for the 'засичам' from PONS electronic dictionary:

засOчам нсв III, засекM св I-2.1.
I. прх
1. (определям, отбелязвам) locate;
радарите засякоха самолета the radars located the plane;
засечи ми времето time me
2. (заварвам, намирам) catch, find;
~ нкг някъде find sb somewhere
3. разг (прекъсвам нкг) interrupt;
засякох го с неочакван въпрос he was caught out by my unexpected question
4. (съпоставям) compare, collate;
~ данни/показания collate data/measurements
II. нпрх (блокирам) misfire;
пистолетът засече the gun misfired;
мисълта ми засече my mind went blank
III. рефл: ~ се (срещаме се) run into;
засякохме се на партито we ran into each other at the party

In my opinion (based on these meanings and on common logic - in which the meaning of the concrete context also plays a certain role), it should be understood as "taking bearings" or "surveying", rather than physically "cutting into" the mountain. Actually, I cannot think of an instance in Bulgarian in which 'засичам' would mean physically "cutting into". I hope this helps.

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Note added at 6 days (2008-09-27 21:02:51 GMT) Post-grading
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Thank you, Mark!