The depth is the 4th column, though that may not be correct if your reads are paired-end. You could find the location of the maximum with a simple awk script:

samtools mpileup ...options... foo.bam | awk '{if($4 > maxdepth) {chr=$1; pos=$2; maxdepth=$4;}}END{print chr,pos,maxdepth}'

One option is to use BEDOPS and format your regions-of-interest into a BED file called regions.bed:

$ bam2bed < foo.bam | bedmap --echo --max-element regions.bed - > answer.bed

The bam2bed script converts the BAM file to BED and pipes it to bedmap, which uses the score operator --max-element to return the maximum scoring BAM element over each region in regions.bed.