Why does this MySQL query take so long and not use the Primary Key index on the join?

I'm joining two tables in a MySQL query ( simplified version below ). This query takes ~10sec to execute. Both tables have about a million rows. Properties has a lot of data and is 2GB while geospatial is ~200MB. Geospatial's primary key is mls_id and properties has non-unique indexes on mls_id and rets_feed.

If I remove the and properties.rets_feed = 'san_fran' or the and properties.mls_id < 100 portion of the query, it executes ~100x faster ( ~110ms ). My actual query from my application has a lot more WHERE's and a bunch of HAVING's based on some calculations made in the SELECT statement, but I think I've isolated the processing-time issue to this smaller example query below.

The Query:

SELECT
    properties.mls_id,
    geospatial.geocoded_address
FROM
    properties,
    geospatial
WHERE
    geospatial.mls_id = properties.mls_id
    and properties.rets_feed = 'san_fran'
    and properties.mls_id != '';

The Explain Details:

1   SIMPLE  geospatial  ALL NULL                NULL      NULL  NULL    1089034  NULL
1   SIMPLE  properties  ref mls_id,rets_feed    mls_id    45    func    1        Using index condition; Using where

Properties Table ( abbreviated, cuz it's got 100's of columns ):

CREATE TABLE `properties` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `mls_id` varchar(14) DEFAULT NULL,
  `last_downloaded` datetime NOT NULL,
  `rets_feed` varchar(25) DEFAULT NULL,
  `rets_resource` varchar(25) DEFAULT NULL,
  `rets_class` varchar(4) DEFAULT NULL,
  `address_full` varchar(50) DEFAULT NULL,
  `street_name` varchar(55) DEFAULT NULL,
  `street_number` varchar(10) DEFAULT NULL,
  `city` varchar(100) DEFAULT NULL,
  `county` varchar(30) DEFAULT NULL,
  `state` varchar(30) DEFAULT NULL,
  `zip` varchar(12) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `mls_id` (`mls_id`),
  KEY `rets_feed` (`rets_feed`)
) ENGINE=InnoDB AUTO_INCREMENT=1089499 DEFAULT CHARSET=utf8;

Geospatial Table:

CREATE TABLE `geospatial` (
  `mls_id` varchar(20) NOT NULL DEFAULT '',
  `geocoded_address` varchar(255) DEFAULT NULL,
  `lat` decimal(10,8) DEFAULT NULL,
  `lon` decimal(11,8) DEFAULT NULL,
  `lat_lon` point NOT NULL,
  `street_number` int(11) unsigned DEFAULT NULL,
  `street_name` varchar(50) DEFAULT NULL,
  `street_name_short` varchar(50) DEFAULT NULL,
  `neighborhood` varchar(50) DEFAULT NULL,
  `neighborhood_short` varchar(50) DEFAULT NULL,
  `city` varchar(50) DEFAULT NULL,
  `city_short` varchar(50) DEFAULT NULL,
  `county` varchar(50) DEFAULT NULL,
  `county_short` varchar(50) DEFAULT NULL,
  `state` varchar(50) DEFAULT NULL,
  `state_short` varchar(2) DEFAULT NULL,
  `country` varchar(50) DEFAULT NULL,
  `country_short` varchar(2) DEFAULT NULL,
  `zip` int(5) unsigned DEFAULT NULL,
  `zip_plus_four` int(4) unsigned DEFAULT NULL,
  `last_geocoded` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
  `source` varchar(25) NOT NULL DEFAULT '',
  `geocodio_accuracy` decimal(3,2) unsigned DEFAULT NULL,
  PRIMARY KEY (`mls_id`),
  KEY `last_geocoded` (`last_geocoded`),
  SPATIAL KEY `lat_lon` (`lat_lon`),
  KEY `street_number` (`street_number`),
  KEY `street_name` (`street_name`),
  KEY `neighborhood` (`neighborhood`),
  KEY `city` (`city`),
  KEY `county` (`county`),
  KEY `state` (`state`),
  KEY `state_short` (`state_short`),
  KEY `zip` (`zip`),
  KEY `zip_plus_four` (`zip_plus_four`),
  KEY `country` (`country`),
  KEY `country_short` (`country_short`),
  KEY `source` (`source`),
  KEY `accuracy` (`geocodio_accuracy`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1;